Display device

ABSTRACT

A display device with low power consumption is provided. Furthermore, a display device in which an image is displayed in a region that can be used in a folded state is provided. The conceived display device includes a display portion that can be opened and folded, a sensing portion that senses a folded state of the display portion, and an image processing portion that generates, when the display portion is in the folded state, an image in which a black image is displayed in part of the display portion.

TECHNICAL FIELD

The present invention relates to an object, a method, or a manufacturingmethod. In addition, the present invention relates to a process, amachine, manufacture, or a composition of matter. In particular, thepresent invention relates to, for example, a human interface, asemiconductor device, a display device, a light-emitting device, a powerstorage device, a driving method thereof, or a manufacturing methodthereof. For example, the present invention particularly relates to adisplay device. In particular, one embodiment of the present inventionrelates to a foldable display device.

BACKGROUND ART

The social infrastructures relating to means for transmittinginformation have advanced. This has made it possible to acquire,process, and send out many pieces and various kinds of information withthe use of an information processor not only at home or office but alsoat other visiting places.

With this being the situation, portable information processors are underactive development.

For example, portable information processors are often used outdoors,and force might be accidentally applied by dropping to the informationprocessors and display devices included in them. As an example of adisplay device that is not easily broken, a display device having highadhesiveness between a structure body by which a light-emitting layersare partitioned and a second electrode layer is known (Patent Document1).

A multi-panel electronic device including the following functions isknown. First acceleration data is received from a first sensor coupledto a first portion of an electronic device. In addition, secondacceleration data is further received from a second sensor coupled to asecond portion of the electronic device, and a position of the firstportion is movable with respect to a position of the second portion.Moreover, a structure of the electronic device is further determined atleast on the basis of part of the first acceleration data and part ofthe second acceleration data (Patent Document 2).

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2012-190794-   [Patent Document 2] Japanese Published Patent Application No.    2012-502372

DISCLOSURE OF INVENTION

An object of one embodiment of the present invention is to provide adisplay device with low power consumption. Another object is to providea display device in which an image is displayed in a region that can beused in a folded state. Another object is to provide a novel displaydevice.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Other objects will be apparent fromand can be derived from the description of the specification, thedrawings, the claims, and the like.

One embodiment of the present invention is a display device including: afoldable display portion including a first region and a second region; asensing portion that senses an opened state or a folded state of thedisplay portion and supplies a fold signal; a control portion thatreceives the fold signal and supplies an image control signal; an imageprocessing portion that receives the image control signal and generatesand supplies an image signal; and a driver circuit that receives theimage signal and drives the display portion. The control portionsupplies the image control signal that makes the image processingportion generate an image in which a black image is displayed in thesecond region of the display portion in a folded state.

Another embodiment of the present invention is the above display devicein which the control portion includes an arithmetic unit and a storageunit that stores a program to be executed by the arithmetic unit. Theprogram includes a first step of allowing interrupt processing; a secondstep of proceeding to a third step when the display portion is in anopened state and proceeding to a fourth step when the display portion isin a folded state; the third step of generating an image to be displayedin the first region and the second region; the fourth step of generatingan image in which a black image is displayed in the second region; afifth step of displaying an image on the display portion; a sixth stepof proceeding to a seventh step when a termination instruction has beensupplied in the interrupt processing and returning to the second stepwhen the termination instruction has not been supplied in the interruptprocessing; and the seventh step of terminating the program. Theinterrupt processing includes an eighth step of allowing operation and aninth step of recovering from the interrupt processing.

The above display device of one embodiment of the present inventionincludes a display portion that can be opened and folded, a sensingportion that senses a folded state of the display portion, and an imageprocessing portion that generates, when the display portion is in thefolded state, an image in which a black image is displayed in part ofthe display portion. Thus, a region where display is unnecessary whenpart of the display portion is folded can display a black image.Consequently, a display device with low power consumption can beprovided. Furthermore, a display device in which an image is displayedin a region that can be used in a folded state can be provided.

Another embodiment of the present invention is a display deviceincluding: a foldable display portion including a first region and asecond region; a sensing portion that senses an opened state or a foldedstate of the display portion and supplies a fold signal; a controlportion that receives the fold signal and supplies an image controlsignal and a synchronization control signal; an image processing portionthat receives the image control signal and generates and supplies afirst image signal and a second image signal; a synchronization signalsupply portion that receives the synchronization control signal andsupplies a first synchronization signal and a second synchronizationsignal; a first driver circuit that receives the first image signal andthe first synchronization signal and drives the first region; and asecond driver circuit that receives the second image signal and thesecond synchronization signal and drives the second region. The controlportion supplies the image control signal that makes the imageprocessing portion generate an image in which a black image is displayedin the second region of the display portion in a folded state and thesynchronization control signal that stops selection of a scan line inthe second region of the display portion in a folded state.

Another embodiment of the present invention is the above display devicein which the control portion includes an arithmetic unit and a storageunit that stores a program to be executed by the arithmetic unit. Theprogram includes a first step of allowing interrupt processing; a secondstep of proceeding to a third step when the display portion is in anopened state and proceeding to a fourth step when the display portion isin a folded state; the third step of proceeding to a fifth step when theopened state has not changed and proceeding to a sixth step when theopened state has changed to the folded state; the fourth step ofproceeding to a seventh step when the folded state has not changed andproceeding to an eighth step when the folded state has changed to theopened state; the fifth step of executing processing 1; the sixth stepof executing processing 2; the seventh step of executing processing 3;the eighth step of executing processing 4; a ninth step of proceeding toa tenth step when a termination instruction has been supplied in theinterrupt processing and returning to the second step when thetermination instruction has not been supplied in the interruptprocessing; and the tenth step of terminating the program. The interruptprocessing includes an eleventh step of allowing operation and a twelfthstep of recovering from the interrupt processing.

Another embodiment of the present invention is the above display devicein which the program includes the following four types of processing.The processing 1 includes a first step of making the synchronizationsignal supply portion supply synchronization signals to the first drivercircuit and the second driver circuit; a second step of making the imageprocessing portion generate an image to be displayed in the first regionand the second region; a third step of making the display portiondisplay the image; and a fourth step of recovering from the processing1. The processing 2 includes a first step of making the synchronizationsignal supply portion supply synchronization signals to the first drivercircuit and the second driver circuit; a second step of making the imageprocessing portion generate an image in which a black image is displayedin the second region; a third step of making the display portion displaythe image; a fourth step of making the synchronization signal supplyportion sequentially stop supply of synchronization signals to thesecond driver circuit; and a fifth step of recovering from theprocessing 2. The processing 3 includes a first step of making thesynchronization signal supply portion supply synchronization signals tothe first driver circuit; a second step of making the image processingportion generate an image to be displayed in the first region; a thirdstep of making the display portion display the image in the firstregion; and a fourth step of recovering from the processing 3. Theprocessing 4 includes a first step of making the synchronization signalsupply portion sequentially supply synchronization signals to the seconddriver circuit; a second step of making the image processing portiongenerate an image to be displayed in the first region and the secondregion; a third step of making the display portion display the image;and a fourth step of recovering from the processing 4.

The above display device of one embodiment of the present inventionincludes a display portion that can be opened and folded, a sensingportion that senses a folded state of the display portion, an imageprocessing portion that generates, when the display portion is in thefolded state, an image in which a black image is displayed in part ofthe display portion, and a synchronization signal supply portion thatcan stop the supply of a synchronization signal used for a portion wherea black image is to be displayed. Thus, the display in a region wheredisplay is unnecessary when part of the display portion is folded can bestopped. Consequently, a display device with low power consumption canbe provided. Furthermore, a display device in which an image isdisplayed in a region that can be used in a folded state can beprovided.

Another embodiment of the present invention is the above display devicefurther including a first power supply that supplies a power supplypotential to the first driver circuit and a second power supply thatsupplies a power supply potential to the second driver circuit. Thecontrol portion supplies a power supply control signal to the secondpower supply in accordance with the fold signal. The second power supplystops supply of a power supply potential in accordance with the powersupply control signal.

The above display device of one embodiment of the present inventionincludes a display portion that can be opened and folded, asynchronization signal supply portion that can stop the supply of asynchronization signal used for a portion where a black image is to bedisplayed, and a power supply that can stop the supply of a power supplypotential used for a portion where a black image is to be displayed.Thus, the display in a region where display is unnecessary when part ofthe display portion is folded can be stopped. Consequently, a displaydevice with low power consumption can be provided. Furthermore, adisplay device in which an image is displayed in a region that can beused in a folded state can be provided.

Another embodiment of the present invention is the above display devicewhich further includes a magnet and in which the sensing portionincludes a magnetic sensor. The magnet is placed at a position such thatthe magnetic sensor can sense an opened state or a folded state of thedisplay portion.

The above display device of one embodiment of the present inventionincludes a display portion that can be opened and folded, a magnet and asensing portion including a magnetic sensor that are placed to sense afolded state of the display portion, and an image processing portionthat generates, when the display portion is in the folded state, animage in which a black image is displayed in part of the displayportion. Thus, a region where display is unnecessary when part of thedisplay portion is folded can display a black image. Moreover, thefolded state can be maintained by a magnetic force of the magnet.Consequently, a display device with low power consumption can beprovided. Furthermore, a display device in which an image is displayedin a region that can be used in a folded state can be provided.

According to one embodiment of the present invention, a display devicewith low power consumption can be provided. Furthermore, a displaydevice in which an image is displayed in a region that can be used in afolded state can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A, 1B1, and 1B2 are a block diagram and schematic viewsillustrating a structure of a display device of an embodiment.

FIGS. 2A and 2B are a block diagram and a circuit diagram illustrating astructure of a display portion in a display device of an embodiment.

FIGS. 3A and 3B are flow charts illustrating the operation of a controlportion in a display device of an embodiment.

FIG. 4 is a block diagram illustrating a structure of a display deviceof an embodiment.

FIGS. 5A and 5B are flow charts illustrating the operation of a controlportion in a display device of an embodiment.

FIGS. 6A to 6D are flow charts each illustrating a processing performedby a control portion in a display device of an embodiment.

FIGS. 7A to 7C are external views illustrating a structure of a displaydevice of an embodiment.

FIGS. 8A to 8D illustrate a structure of a display device of anembodiment.

FIGS. 9A and 9B illustrate a structure of a display panel that can beused for a display device of an embodiment.

FIGS. 10A to 10C illustrate a structure of a transistor that can be usedin a display device of an embodiment.

FIGS. 11A to 11C illustrate a structure of a display panel that can beused for a display device of an embodiment.

FIGS. 12A and 12B illustrate a structure of a display panel that can beused for a display device of an embodiment.

FIG. 13 illustrates a structure of a display panel that can be used fora display device of an embodiment.

FIG. 14 is a block diagram illustrating a structure of a display portionin a display device of an embodiment.

FIGS. 15A and 15B are a block diagram and a circuit diagram illustratinga structure of a display portion in a display device of an embodiment.

FIG. 16 is a block diagram illustrating a structure of a display deviceof an embodiment.

FIG. 17 is a block diagram illustrating a structure of a display deviceof an embodiment.

FIG. 18 is a block diagram illustrating a structure of a display deviceof an embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that various changesand modifications can be made without departing from the spirit andscope of the present invention. Therefore, the present invention shouldnot be construed as being limited to the description in the followingembodiments. Note that in the structures of the invention describedbelow. the same portions or portions having similar functions aredenoted by the same reference numerals in different drawings, anddescription of such portions is not repeated.

Embodiment 1

In this embodiment, a structure of a display device of one embodiment ofthe present invention is described with reference to FIGS. 1A, 1B1, and1B2, FIGS. 2A and 2B, and FIGS. 3A and 3B.

FIGS. 1A, 1B1, and 1B2 are a block diagram and schematic viewsillustrating the structure of the display device of one embodiment ofthe present invention.

FIGS. 2A and 2B illustrate a display portion that can be used in thedisplay device of one embodiment of the present invention. FIG. 2A is ablock diagram illustrating the structure of the display portion, andFIG. 2B is a circuit diagram illustrating a pixel circuit in which anelectroluminescent (EL) element is used as a display element.

FIGS. 3A and 3B are flow charts illustrating the operation of a controlportion of the display device of one embodiment of the presentinvention. FIG. 3A is a flow chart illustrating main processing, andFIG. 3B is a flow chart illustrating interrupt processing.

A display device 200 described in this embodiment includes a foldabledisplay portion 230 including a first region 230(1) and a second region230(2); a sensing portion 240 that senses an opened state or a foldedstate of the display portion 230 and supplies a fold signal F; a controlportion 210 that receives the fold signal F and supplies an imagecontrol signal VC; an image processing portion 220 that receives theimage control signal VC and supplies an image signal VIDEO; and drivercircuits 232 that receive the image signal VIDEO and drive the displayportion 230 (see FIG. 1A). Note that the first region 230(1) refers to aregion seen from a user regardless of an opening state and a foldedstate. Further, the second region 230(2) refers to a region that isinside in a folded sate and is not seen from a user.

The control portion 210 supplies the image control signal VC that makesthe image processing portion 220 generate an image in which a blackimage is displayed in the second region 230(2) of the display portion230 in a folded state.

The control portion 210 of the display device 200 described in thisembodiment includes an arithmetic unit and a storage unit that stores aprogram to be executed by the arithmetic unit. The program includes thefollowing steps.

In a first step, the interrupt processing is allowed (FIG. 3A (Q1)).Note that when the interrupt processing is allowed, the arithmetic unitcan receive an instruction to execute the interrupt processing. Thearithmetic unit that has received the instruction to execute theinterrupt processing stops the main processing and executes theinterrupt processing. For example, the arithmetic unit that has receivedan event associated with the instruction stops the main processing,executes the interrupt processing, and stores the execution result ofthe interrupt processing in the storage unit. Then, the arithmetic unitthat has recovered from the interrupt processing can resume the mainprocessing on the basis of the execution result of the interruptprocessing.

In a second step, the operation proceeds to a third step when thedisplay portion 230 is in an opened state and proceeds to a fourth stepwhen the display portion 230 is in a folded state (FIG. 3A (Q2)).Specifically, a fold signal F is acquired and is used to determinewhether the display portion 230 is in an opened state or in a foldedstate.

In the third step, an image to be displayed in the first region 230(1)and the second region 230(2) is generated (FIG. 3A (Q3)). Note thatsince the display portion 230 is opened, an image can be displayed usingthe entire display portion 230, that is, the first region 230(1) and thesecond region 230(2).

In the fourth step, an image in which a black image is displayed in thesecond region 230(2) is generated (FIG. 3A (Q4)). Note that since thedisplay portion 230 is folded, an image can be displayed using part ofthe display portion 230, that is, only the first region 230(1).

In a fifth step, an image is displayed in the display portion 230 (FIG.Q5)).

In a sixth step, the operation proceeds to a seventh step when atermination instruction has been supplied in the interrupt processingand returns to the second step when the termination instruction has notbeen supplied in the interrupt processing (FIG. 3A (Q6)).

In the seventh step, the program is terminated (FIG. 3A (Q7)).

The interrupt processing includes an eighth step of allowing operationand a ninth step of recovering from the interrupt processing (FIG. 3B(R8) and (R9)). Note that a variety of operations can be performed inthe interrupt processing. For example, a user of the display device 200can give an instruction to select an image to be displayed or aninstruction to terminate the program.

The above display device 200 of one embodiment of the present inventionincludes the display portion 230 that can be opened and folded, thesensing portion 240 that senses a folded state of the display portion230, and the image processing portion 220 that generates, when thedisplay portion 230 is in the folded state, an image in which a blackimage is displayed in part of the display portion 230. Thus, a regionwhere display is unnecessary when part of the display portion 230 isfolded can display a black image. Consequently, a display device withlow power consumption can be provided. Furthermore, a display device inwhich an image is displayed in a region that can be used in a foldedstate can be provided.

In addition, the display device 200 described as an example in thisembodiment includes a power supply portion 214 that supplies powersupply potential to the driver circuits 232 and a synchronization signalsupply portion 212 that supplies a synchronization signal SYNC to thedriver circuits 232.

The driver circuits 232 include a scan line driver circuit 232G and asignal line driver circuit 232S. Note that as shown in FIG. 14, the scanline driver circuit 232G and the signal line driver circuit 232S in FIG.1A may be replaced with each other. Similarly, as shown in FIG. 15A, thescan line driver circuit 232G and the signal line driver circuit 232S inFIG. 2A may be replaced with each other. In that case, as shown in FIG.15B, a pixel 631 p is rotated by 90°.

The sensing portion 240 senses a sign 239 and senses a folded state ofthe display portion 230.

The sign 239 is placed, for example, in the vicinity of the displayportion 230 so that the positional relation between the sign 239 and thesensing portion 240 changes in accordance with the opened state or thefolded state of the display portion 230. Thus, the sensing portion 240can sense the opened state or the folded state of the display portion230 and supply a fold signal F.

Elements included in the display device 200 of one embodiment of thepresent invention are described below.

<<Foldable Display Portion>>

The foldable display portion 230 includes the first region 230(1) andthe second region 230(2). The display portion 230 includes a displaypanel provided with display elements and a housing supporting thedisplay panel.

The display panel includes a pixel portion in the first region 230(1)and the second region 230(2). Pixels are arranged such that a continuousimage is displayed in the first region 230(1) and the second region230(2). For example, pixels are arranged at regular intervals throughoutthe first and second regions so that a user does not recognize aboundary 230 b(1) between the first region 230(1) and the second region230(2) (see FIG. 1A).

The pixel portion includes a plurality of pixels, a plurality of scanlines, and a plurality of signal lines.

Each of the pixels includes a pixel circuit electrically connected toone scan line and one signal line and a display element electricallyconnected to the pixel circuit.

A display panel that can be used for the foldable display portion 230includes, for example, a flexible substrate and display elements overthe substrate. For example, the display panel can be bent with acurvature radius of greater than or equal to 1 mm and less than or equalto 100 mm with one surface on which an image can be displayed facingeither inward or outward. Specifically, the display panel can have astructure in which an inorganic film provided with pixels is sandwichedbetween flexible films.

A housing that can be used for the foldable display portion 230 includesa hinge that can be folded at, for example, the boundary 230 b(1) (seeFIGS. 1B1 and 1B2).

The display portion 230 described in this embodiment is foldable inthree parts; however, one embodiment of the present invention is notlimited to such a structure. Specifically, the display portion 230 maybe foldable in two parts or in four or more parts. A larger foldablenumber leads to a smaller external shape in a folded state, resulting inhigher portability.

The display portion 230 can be folded at the boundary 230 b(1) betweenthe first region 230(1) and the second region 230(2).

FIG. 1B1 illustrates a state where the display portion 230 is openedflat.

FIG. 1B2 schematically illustrates a state where the display portion 230is bent, specifically, a state where the display portion 230 is bentoutward at the boundary 230 b(1) and bent inward at a boundary 230 b(2)so as to be folded in three parts.

In particular, in a folded state of the display device 200, the firstregion 230(1) is preferably placed on the outer side of the displaydevice 200. In that case, a user can see an image displayed in the firstregion 230(1) in a folded state.

Note that an example of a structure of the foldable display portion 230is described in detail in Embodiment 3.

<<Driver Circuit>>

The driver circuits 232 include the scan line driver circuit 232G andthe signal line driver circuit 232S. The driver circuits 232 can beformed using, for example, any of a variety of sequential circuits suchas a shift register. In the case where a driver circuit that is formedusing an LSI is placed in a flexible display portion, the driver circuitis placed in a portion other than a bendable portion. Note that a drivercircuit that can be formed in the same process as the pixel circuit ispreferable because it can be placed in a bendable portion of a flexibledisplay portion and therefore has a small limit in its position.

The scan line driver circuit 232G receives power supply potential and asynchronization signal SYNC and supplies a scan line selection signal.

The signal line driver circuit 232S receives power supply potential, asynchronization signal SYNC, and an image signal VIDEO and supplies animage signal.

A scan line selection signal is supplied to the display portion 230,whereby one scan line and pixels connected to the scan line areselected.

Image signals are supplied to pixels to which a scan line selectionsignal is supplied, and pixel circuits in the pixels store the imagesignals. In addition, display elements in the pixels perform display inaccordance with the image signals.

<<Synchronization Signal Supply Portion>>

The synchronization signal supply portion 212 supplies a synchronizationsignal SYNC. The synchronization signal SYNC is used for synchronousoperation of the driver circuits 232. Examples of the synchronizationsignal SYNC include a vertical synchronization signal and a horizontalsynchronization signal, a start pulse signal SP, a latch signal LP, apulse width control signal PWC, and a clock signal CLK.

<<Power Supply Portion>>

The power supply portion 214 supplies power supply potential. As thepower supply potential, at least one of a high power supply potential(e.g., VDD) and a low power supply potential (e.g., VSS or GND) can besupplied. There is also a case where a plurality of high power supplypotentials (e.g., VDD1 and VDD2) are supplied.

<<Image Processing Portion>>

The image processing portion 220 receives an image control signal VC,generates an image, and supplies an image signal VIDEO of the generatedimage.

The image signal VIDEO includes data on an image to be displayed in thefirst region 230(1) and the second region 230(2) of the display portion230.

For example, the image processing portion 220 can generate, inaccordance with the image control signal VC, one image to be displayedin the first region 230(1) and the second region 230(2). Moreover, theimage processing portion 220 can generate, in accordance with the imagecontrol signal VC, one image in which a black image, for example, isdisplayed in the second region 230(2). For example, an image with thedarkest gray level among gray levels that can be displayed by displayelements is referred to as a black image.

When display elements display a black image, power consumption can bemade lower than that for displaying other images (e.g., a white image ora gray image), resulting in a reduction in the power consumption of thedisplay device 200.

Specifically, power consumed by the second region 230(2) that is foldedso that display cannot be seen can be reduced.

A light-emitting element is an example of a display element thatconsumes less power when displaying a black image than when displayingother images. Note that in the case where display elements consume theleast power at a gray level different from the darkest gray level thatcan be displayed by the display elements, an image with that gray levelmay be displayed instead of a black image.

<<Sensing Portion and Sign>>

The sensing portion 240 senses an opened state or a folded state of thedisplay portion 230 and supplies a fold signal F. Note that the foldsignal F includes data indicating an opened state or data indicating afolded state.

The sensing portion 240 is provided with a sensor that senses the sign239 that is close thereto. The sensor senses the sign 239 placed in thevicinity of the display portion 230, whereby the sensing portion 240 cansupply a fold signal F corresponding to the folded state of the displayportion 230.

For example, the shape or place of an object such as a protrusion, anelectromagnetic wave such as light, an electric wave, or a magneticforce, or the like can serve as the sign 239. Specifically, the aboveserving as the sign 239 may have different polarities (e.g., the N- andS-poles of a magnet) or different signals (e.g., electromagnetic waveswhich are modulated by different methods), for example.

A sensor that can identify the sign 239 is selected as the sensorincluded in the sensing portion 240.

Specifically, in the case where a structure having different shapes orin different places (e.g., a protrusion) is used as the sign 239, aswitch or the like having different shapes or in different places can beused for the sensor so that the structure can be identified.Alternatively, in the case where light is used as the sign 239, aphotoelectric conversion element or the like can be used for the sensor.In the case where an electric wave is used as the sign 239, an antennaor the like can be used for the sensor. In the case where a magnet isused as the sign 239, a magnetic sensor or the like can be used for thesensor.

Note that the sensing portion 240 may sense acceleration, a direction, aglobal positioning system (GPS) signal, temperature, humidity, or thelike and supply data thereon in addition to the fold signal F.

A structure in which a magnet is used as the sign 239 and a magneticsensor that senses a magnetic force of the magnet is used for thesensing portion 240 will be described.

The display device 200 includes a magnet as the sign 239, and thesensing portion 240 includes a magnetic sensor. The magnet is placed ata position such that the magnetic sensor can sense an opened state or afolded state of the display portion 230.

The display device 200 described in this embodiment includes the displayportion 230 that can be opened and folded, a magnet (the sign 239) andthe sensing portion 240 including a magnetic sensor that are placed tosense a folded state of the display portion 230, and the imageprocessing portion 220 that generates, when the display portion is inthe folded state, an image in which a black image is displayed in partof the display portion 230 (specifically, the second region). Thus, aregion (specifically, the second region) where display is unnecessarywhen part of the display portion 230 is folded can display a blackimage. Moreover, the folded state can be maintained by a magnetic forceof the magnet. Consequently, a display device with low power consumptioncan be provided. Furthermore, a display device in which an image isdisplayed in a region that can be used in a folded state can beprovided. Furthermore, a display device that is prevented from beingchanged from a folded state to an opened state unintentionally can beprovided.

<<Control Portion>>

The control portion 210 can receive a fold signal F and supply an imagecontrol signal VC. The control portion 210 may also supply signals forcontrolling the power supply portion 214 and the synchronization signalsupply portion 212.

The image control signal VC is a signal for controlling the imageprocessing portion 220. Examples of the image control signal VC includea signal that makes the image processing portion 220 generate differentimages in accordance with the opened state or the folded state of thedisplay portion 230.

<<Timing Generator>>

A timing generator generates and supplies a reference clock signal orthe like that the display device 200 needs.

<<Structure of Display Portion 230>>

The display portion 230 includes a plurality of pixels 631 p and wiringsthat connect the plurality of pixels 631 p (see FIG. 2A and FIG. 15A).Note that the kinds and number of the wirings are determined asappropriate depending on the structure. number, and arrangement of thepixels 631 p.

Each of the pixels 631 p is electrically connected to at least one scanline and one signal line.

For example, in the case where the pixels 631 p are arranged in a matrixof x columns and y rows in the display portion 230, signal lines S1 toSx and scan lines G1 to Gy are provided in the display portion 230 (seeFIG. 2A and FIG. 15A). The scan lines G1 to Gy can supply scan lineselection signals to the respective rows. The signal lines S1 to Sx cansupply image signals to pixels to which a scan line selection signal issupplied.

<<Structure of Pixel 631 p>>

The pixel 631 p includes a display element and a pixel circuit includingthe display element.

The pixel circuit holds the supplied image signal and makes the displayelement display a gray level corresponding to the image signal. Notethat the structure of the pixel circuit is selected as appropriate inaccordance with the kind or the driving method of the display element.

As the display element, an EL element, electronic ink utilizingelectrophoresis, a liquid crystal element, or the like can be used.

FIG. 2B and FIG. 15B each illustrate, as an example of the pixelcircuit, a structure in which an EL element is used as the displayelement.

A pixel circuit 634EL includes a first transistor 634 t_1 including agate electrode electrically connected to a scan line G through which ascan line selection signal can be supplied, a first electrodeelectrically connected to a signal line S through which an image signalcan be supplied, and a second electrode electrically connected to afirst electrode of a capacitor 634 c.

The pixel circuit 634EL also includes a second transistor 634 t_2including a gate electrode electrically connected to a second electrodeof the first transistor 634 t_1, a first electrode electricallyconnected to a second electrode of the capacitor 634 c, and a secondelectrode electrically connected to a first electrode of an EL element635EL.

The second electrode of the capacitor 634 c and the first electrode ofthe second transistor 634 t_2 are electrically connected to a wiring Athrough which power supply potential and a potential needed for lightemission of the EL element 635EL can be supplied. Note that thepotential of the wiring A may be constant or may change in a pulsedmanner every certain period. A second electrode of the EL element 635ELis electrically connected to a wiring C through which a common potentialcan be supplied. Note that the difference between the power supplypotential and the common potential is larger than the emission startvoltage of the EL element 635EL.

The EL element 635EL includes a layer containing a light-emittingorganic compound between a pair of electrodes.

<<Transistor>>

The second transistor 634 t_2 supplies a current corresponding to thepotential of the signal line S to control the light emission of the ELelement 635EL. The second transistor 634 t_2 includes silicon, an oxidesemiconductor, or the like in a region where a channel is formed.

As an example of a transistor that can be suitably used as the firsttransistor 634 t_1 or the second transistor 634 t_2, a transistorincluding an oxide semiconductor can be given.

A transistor including an oxide semiconductor film can have leakagecurrent between a source and a drain in an off state (off-state current)much lower than that of a conventional transistor including silicon. Anexample of a structure of the transistor that can be suitably used asthe first transistor 634 t_1 or the second transistor 634 t_2 isdescribed in Embodiment 4.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 2

In this embodiment, a structure of a display device of one embodiment ofthe present invention is described with reference to FIG. 4, FIGS. 5Aand 5B, and FIGS. 6A to 6D.

FIG. 4 is a block diagram illustrating the structure of the displaydevice of one embodiment of the present invention.

FIGS. 5A and 5B are flow charts illustrating the operation of a controlportion of the display device of one embodiment of the presentinvention. FIG. 5A is a flow chart illustrating main processing, andFIG. 5B is a flow chart illustrating interrupt processing.

FIGS. 6A to 6D are flow charts illustrating processing 1, processingprocessing 3, and processing 4 performed by the control portion of thedisplay device of one embodiment of the present invention.

A display device 200B described in this embodiment includes the foldabledisplay portion 230 including the first region 230(1) and the secondregion 230(2); the sensing portion 240 that senses an opened state or afolded state of the display portion 230 and supplies a fold signal F; acontrol portion 210B that receives the fold signal F and supplies animage control signal VC and a synchronization control signal SC; theimage processing portion 220 that receives the image control signal VCand supplies a first image signal VIDEO(1) and a second image signalVIDEO(2); the synchronization signal supply portion 212 that receivesthe synchronization control signal SC and supplies a firstsynchronization signal SYNC(1) and a second synchronization signalSYNC(2); a first driver circuit 232(1) that receives the first imagesignal VIDEO(1) and the first synchronization signal SYNC(1) and drivesthe first region 230(1); and a second driver circuit 232(2) thatreceives the second image signal VIDEO(2) and the second synchronizationsignal SYNC(2) and drives the second region 230(2).

The control portion 210B supplies the image control signal VC that makesthe image processing portion 220 generate an image in which a blackimage is displayed in the second region 230(2) of the display portion230 in a folded state and the synchronization control signal SC thatstops selection of a scan line in the second region 230(2) of thedisplay portion 230 in a folded state.

The control portion 210B of the display device 200B described in thisembodiment includes an arithmetic unit and a storage unit that stores aprogram to be executed by the arithmetic unit. The program includes thefollowing steps.

In a first step, the interrupt processing is allowed (FIG. 5A (S1)).

In a second step, the operation proceeds to a third step when thedisplay portion 230 is in an opened state and proceeds to a fourth stepwhen the display portion 230 is in a folded state (FIG. 5A (S2)).Specifically, a fold signal F is acquired and is used to determinewhether the display portion 230 is in an opened state or in a foldedstate.

In the third step, the operation proceeds to a fifth step in the casewhere the opened state of the display portion 230 has not changed, andproceeds to a sixth step in the case where the opened state of thedisplay portion 230 has changed to the folded state (FIG. 5A (S3)). Notethat a fold signal F that was acquired in the second step just prior tothis step is compared with a fold signal F that was stored in thestorage unit previously, whereby it is determined whether or not therehas been a change in the state. In the case where the opened state ofthe display portion 230 has changed, a new fold signal F is stored toupdate the storage unit.

In the fourth step, the operation proceeds to a seventh step in the casewhere the folded state of the display portion 230 has not changed, andproceeds to an eighth step in the case where the folded state of thedisplay portion 230 has changed to the opened state (FIG. 5A (S4)). Notethat a fold signal F that was acquired in the second step just prior tothis step is compared with a fold signal F that was stored in thestorage unit previously, whereby it is determined whether or not therehas been a change in the state. In the case where the folded state ofthe display portion 230 has changed, a new fold signal F is stored toupdate the storage unit.

In the fifth step, the processing 1 is executed (FIG. 5A (S5)).

In the sixth step, the processing 2 is executed (FIG. 5A (S6)).

In the seventh step, the processing 3 is executed (FIG. 5A (S7)).

In the eighth step, the processing 4 is executed (FIG. 5A (S8)).

In a ninth step, the operation proceeds to a tenth step when atermination instruction has been supplied in the interrupt processingand returns to the second step when the termination instruction has notbeen supplied in the interrupt processing (FIG. 5A (S9)).

In the tenth step, the program is terminated (FIG. 5A (S10)).

The interrupt processing includes an eleventh step of allowing operationand a twelfth step of recovering from the interrupt processing (FIG. 5B(T11) and (T12)).

The control portion 210B of the display device 200B described in thisembodiment includes the storage unit that stores a program for executionof four types of processing. The program for execution of the four typesof processing includes the following steps.

<<Processing 1>>

In a first step of the processing 1, the arithmetic unit makes thesynchronization signal supply portion 212 supply a first synchronizationsignal SYNC(1) to the first driver circuits 232(1) and a secondsynchronization signal SYNC(2) to the second driver circuits 232(2)(FIG. 6A (U1)).

In a second step, the arithmetic unit makes the image processing portion220 generate an image to be displayed in the first region 230(1) and thesecond region 230(2) (FIG. 6A (U2)).

In a third step, the arithmetic unit makes the display portion 230display the image (FIG. 6A (U3)).

In a fourth step, the operation recovers from the processing (FIG. 6A(U4)).

<<Processing 2>>

In a first step of the processing 2, the arithmetic unit makes thesynchronization signal supply portion 212 supply a first synchronizationsignal SYNC(1) to the first driver circuits 232(1) and a secondsynchronization signal SYNC(2) to the second driver circuits 232(2)(FIG. 6B (V1)).

In a second step, the arithmetic unit makes the image processing portion220 generate an image in which a black image is displayed in the secondregion 230(2) (FIG. 6B (V2)).

In a third step, the arithmetic unit makes the display portion 230display the image (FIG. 6B (V3)).

In a fourth step, the arithmetic unit makes the synchronization signalsupply portion 212 sequentially stop the supply of the secondsynchronization signals SYNC(2) to the second driver circuits 232(2)(FIG. 6B (V4)).

For example, the supply of synchronization signals is sequentiallystopped in the following order: the potential of a start pulse signal isfixed at “Low”, the potential of a clock signal is fixed at “Low”, andthen the power supply potential is fixed at “Low”.

In a fifth step, the operation recovers from the processing 2 (FIG. 6B(V5)).

<<Processing 3>>

In a first step of the processing 3, the arithmetic unit makes thesynchronization signal supply portion 212 supply a first synchronizationsignal SYNC(1) to the first driver circuits 232(1) (FIG. 6C (W1)).

In a second step, the arithmetic unit makes the image processing portion220 generate an image to be displayed in the first region 230(1) (FIG.6C (W2)).

In a third step, the arithmetic unit makes the display portion 230display the image in the first region 230(1) (FIG. 6C (W3)).

In a fourth step, the operation recovers from the processing 3 (FIG. 6C(W4)).

<<Processing 4>>

In a first step of the processing 4, the arithmetic unit makes thesynchronization signal supply portion 212 sequentially resume the supplyof the second synchronization signals SYNC(2) to the second drivercircuits 232(2) (FIG. 6D (X1)).

For example, the supply of synchronization signals is sequentiallyresumed in the following order: a predetermined power supply potentialis supplied, a clock signal is supplied, and then a start pulse signalis supplied.

In a second step, the arithmetic unit makes the image processing portion220 generate an image to be displayed in the first region 230(1) and thesecond region 230(2) (FIG. 6D (X2)).

In a third step, the arithmetic unit makes the display portion 230display the image (FIG. 6D (X3)).

In a fourth step, the operation recovers from the processing 4 (FIG. 6D(X4)).

The above display device 200B of one embodiment of the present inventionincludes the display portion 230 that can be opened and folded, thesensing portion 240 that senses a folded state of the display portion230, the image processing portion 220 that generates, when the displayportion 230 is in the folded state, an image in which a black image isdisplayed in part of the display portion 230, and the synchronizationsignal supply portion 212 that can stop the supply of a secondsynchronization signal SYNC(2) used for a portion where a black image isto be displayed. Thus, the display in a region where display isunnecessary when part of the display portion is folded can be stopped.Consequently, a display device with low power consumption can beprovided. Furthermore, a display device in which an image is displayedin a region that can be used in a folded state can be provided.

Elements included in the display device 200B of one embodiment of thepresent invention are described below. For elements that can be similarto those in the display device 200 described in Embodiment 1, thedescription in Embodiment 1 can be referred to.

<<Foldable Display Portion>>

The display portion 230 that can be used in the display device 200B canbe similar to the display portion 230 described in Embodiment 1 exceptthat the first region 230(1) is driven by the first driver circuits232(1) and the second region 230(2) is driven by the second drivercircuits 232(2).

Scan lines provided in the first region 230(1) and scan lines providedin the second region 230(2) are electrically insulated from each otherat the boundary 230 b(1) between the first region 230(1) and the secondregion 230(2). Note that in the case where the scan line driver circuit232G is placed on only one side as shown in FIG. 16, the scan lines inthe first region 230(1) and the scan lines in the second region 230(2)may be connected to each other. In that case, since the scan lines inthe second region 230(2) are also selected when the scan lines in thefirst region 230(1) are selected, if black display is to be performed inthe second region 230(2), signals for black display need to be suppliedfrom the signal line driver circuit 232S(2). However, since keepingblack display requires only supply of a constant voltage, powerconsumption can be reduced.

<<Driver Circuit>>

The display device 200B includes the first driver circuits 232(1) andthe second driver circuits 232(2).

The first driver circuits 232(1) include a scan line driver circuit232G(1) and a signal line driver circuit 232S(1).

The second driver circuits 232(2) include a scan line driver circuit232G(2) and a signal line driver circuit 232S(2).

Like FIG. 14 and FIGS. 15A and 15B, FIG. 17 illustrates the case wherethe scan line driver circuits and the signal line driver circuits inFIG. 4 are replaced with each other. In this case, signal lines providedin the first region 230(1) and signal lines provided in the secondregion 230(2) are electrically insulated from each other at the boundary230 b(1) between the first region 230(1) and the second region 230(2).Note that in the case where the signal line driver circuit 232S isplaced on only one side as shown in FIG. 18, the signal lines in thefirst region 230(1) and the signal lines in the second region 230(2) maybe connected to each other. In that case, since image signals aresupplied also to the signal lines in the second region 230(2) when imagesignals are supplied to the signal lines in the first region 230(1), ifblack display is to be performed in the second region 230(2), signalsfor not selecting pixels need to be supplied from the scan line drivercircuit 232G(2). However, since keeping a non-selection state requiresonly supply of a constant voltage, power consumption can be reduced.

The scan line driver circuit 232G(1) receives power supply potential anda first synchronization signal SYNC(1) and supplies scan line selectionsignals to scan lines provided in the first region 230(1).

The scan line driver circuit 232G(2) receives power supply potential anda second synchronization signal SYNC(2) and supplies scan line selectionsignals to scan lines provided in the second region 230(2).

The signal line driver circuit 232S(1) receives power supply potential,a first synchronization signal SYNC(1), and a first image signalVIDEO(1) and supplies an image signal.

The signal line driver circuit 232S(2) receives power supply potential,a second synchronization signal SYNC(2), and a second image signalVIDEO(2) and supplies an image signal.

A scan line selection signal is supplied to the first region 230(1) ofthe display portion 230, whereby one scan line and pixels connected tothe scan line are selected. In addition, a scan line selection signal issupplied to the second region 230(2) of the display portion 230, wherebyone scan line and pixels connected to the scan line are selected.

Image signals are supplied to pixels to which a scan line selectionsignal is supplied, and pixel circuits in the pixels store the imagesignals. In addition, display elements in the pixels perform display inaccordance with the image signals.

<<Synchronization Signal Supply Portion>>

The synchronization signal supply portion 212 receives a synchronizationcontrol signal SC and supplies a first synchronization signal SYNC(1)and a second synchronization signal SYNC(2).

The first synchronization signal SYNC(1) is used for synchronousoperation of the first driver circuits 232(1). The secondsynchronization signal SYNC(2) is used for synchronous operation of thesecond driver circuits 232(2). Examples of the synchronization signalinclude a vertical synchronization signal and a horizontalsynchronization signal, a start pulse signal SP, a latch signal LP, apulse width control signal PWC, and a clock signal CLK.

The synchronization signal supply portion 212 supplies the secondsynchronization signal SYNC(2) or stops the supply in accordance withthe supplied synchronization control signal SC. By stopping the supplyof the second synchronization signal SYNC(2), the operation of thesecond region 230(2) can be stopped. Note that “operation is stopped”refers to the case where wirings in the portion are in a high-impedancestate (or floating state) or to the case where a predetermined potentialis supplied to the wirings and the potential remains constant so thatthe portion is kept in the same state.

<<Image Processing Portion>>

The image processing portion 220 receives an image control signal VC,generates an image, and supplies a first image signal VIDEO(1) and asecond image signal VIDEO(2) of the generated image.

The first image signal VIDEO(1) includes data on an image to bedisplayed in the first region 230(1) of the display portion 230. Thesecond image signal VIDEO(2) includes data on an image to be displayedin the second region 230(2) of the display portion 230.

For example, the image processing portion 220 can generate, inaccordance with the image control signal VC, one image to be displayedin the first region 230(1) and the second region 230(2).

Moreover, the image processing portion 220 can generate, in accordancewith the image control signal VC, one image in which a black image, forexample, is displayed in the second region 230(2).

Furthermore, in accordance with the image control signal VC, the imageprocessing portion 220 can generate only one image to be displayed inthe first region 230(1).

Accordingly, the power consumption of the display device 200B can bereduced.

Specifically, power consumed by the second region 230(2) that is foldedso that display cannot be seen can be reduced.

A light-emitting element is an example of a display element thatconsumes less power when displaying a black image than when displayingother images.

<<Sensing Portion and Sign>>

The sensing portion 240 senses an opened state or a folded state of thedisplay portion 230 and supplies a fold signal F. Note that structuressimilar to those in Embodiment 1 can be used for the sensing portion andthe sign.

<<Control Portion>>

The control portion 210B can receive a fold signal F and supply an imagecontrol signal VC, a synchronization control signal SC, and a powersupply control signal PC.

The image control signal VC is a signal for controlling the imageprocessing portion 220. Examples of the image control signal VC includea signal that makes the image processing portion 220 generate differentimages in accordance with the opened state or the folded state of thedisplay portion 230.

<<Timing Generator>>

A timing generator generates and supplies a reference clock signal orthe like that the display device 200B needs.

<<Power Supply Portion>>

The power supply portion 214 receives a power supply control signal PCand supplies power supply potential.

The power supply portion 214 supplies power supply potential or stopsthe supply in accordance with the supplied power supply control signalPC. By stopping the supply of the power supply potential to the seconddriver circuits 232(2), power consumed by the second driver circuits232(2) can be reduced.

Note that “supply of power supply potential is stopped” sometimes refersto the following case: impedance to at least one of a high power supplypotential (e.g., VDD) and a low power supply potential (e.g., VSS orGND) is made high so that energy is not supplied, and energy of theother power supply potential is supplied. In that case, only the otherpower supply potential is supplied from the driver circuit. As a result,a predetermined potential is supplied to wirings in the portionconnected to the driver circuit and the potential remains constant sothat the portion is kept in the same state.

For example, in the case where only a non-selection signal is to besupplied from the scan line driver circuit 232G(2), only a power supplypotential corresponding to the potential of the non-selection signal issupplied to the scan line driver circuit 232G(2) from the power supplyportion 214. Consequently, current hardly flows in the scan line drivercircuit 232G(2); thus, power consumption can be reduced. Alternatively,in the case where only a potential needed for black display is to besupplied from the signal line driver circuit 232S(2), only a powersupply potential corresponding to the potential needed for black displayis supplied to the signal line driver circuit 232S(2) from the powersupply portion 214. Consequently, current hardly flows in the signalline driver circuit 232S(2); thus, power consumption can be reduced.

Furthermore, “supply of power supply potential is stopped” sometimesrefers to the following case: impedance to both a high power supplypotential (e.g., VDD) and a low power supply potential (e.g., VSS orGND) is made high so that energy is not supplied. In that case, energyis not supplied from the driver circuit. As a result, wirings in theportion connected to the driver circuit are put in a high-impedancestate (or floating state). Thus, in the case where black display hasbeen performed, the black display state is maintained, so that powerconsumption can be reduced. In addition, since current does not flow inthe driver circuit, power consumption can be reduced.

Note that the power supply portion 214 may include a plurality of powersupplies, specifically a first power supply and a second power supply.

A modification example of the display device 200B described in thisembodiment includes a first power supply that supplies power supplypotential to the first driver circuit 232(1) and a second power supplythat supplies power supply potential to the second driver circuit232(2). The control portion 210B supplies a power supply control signalPC to the second power supply in accordance with the fold signal F. Thesecond power supply stops supply of power supply potential in accordancewith the power supply control signal PC.

The above display device of one embodiment of the present inventionincludes a display portion that can be opened and folded, asynchronization signal supply portion that can stop the supply of asynchronization signal used for a portion where a black image is to bedisplayed, and a power supply that can stop the supply of a power supplypotential used for a portion where a black image is to be displayed.Thus, the display in a region where display is unnecessary when part ofthe display portion is folded can be stopped. Consequently, a displaydevice with low power consumption can be provided. Furthermore, adisplay device in which an image is displayed in a region that can beused in a folded state can be provided.

MODIFICATION EXAMPLE

A display device 200D described as a modification example in thisembodiment will be described with reference to FIG. 4; the displaydevice 200B in FIG. 4 is replaced with the display device 200D.

In the display device 200D described as a modification example in thisembodiment, the frequency of rewriting images in the display portion canbe varied.

Specifically, description is given on a display device which has a firstmode in which a scan line selection signal for selecting a pixel isoutput at a frequency of more than or equal to 30 Hz (30 times persecond), preferably more than or equal to 60 Hz (60 times per second)and less than 960 Hz (960 times per second) and a second mode in whichthe scan line selection signal is output at a frequency of more than orequal to 11.6 μHz (once per day) and less than 0.1 Hz (0.1 times persecond), preferably more than or equal to 0.28 mHz (once per hour) andless than 1 Hz (once per second).

When a still image is displayed with the display device 200D describedas a modification example in this embodiment, the refresh rate can beset to less than 1 Hz, preferably less than or equal to 0.2 Hz. Thisenables display with reduced eye strain on a user. Further, a displayimage can be refreshed at an optimal frequency in accordance with thequality of the image displayed on the display portion. Specifically, indisplaying a still image, the refresh rate can be set lower than that indisplaying a smooth moving image; thus, a still image with less flickercan be displayed. In addition, power consumption can be reduced.

Note that the display device 200D described as a modification example inthis embodiment has the same structure as the display device 200B exceptfor the structures of the control portion, the driver circuits, and thedisplay portion.

<<Driver Circuit>>

The scan line driver circuit 232G(1) and the scan line driver circuit232G(2) each supply scan line selection signals at different frequenciesin accordance with the supplied first synchronization signal SYNC(1) andsecond synchronization signal SYNC(2).

For example, the driver circuit supplies scan line selection signals inthe following modes: a first mode of outputting a scan line selectionsignal at a frequency of more than or equal to 30 Hz (30 times persecond), preferably more than or equal to 60 Hz (60 times per second)and less than 960 Hz (960 times per second) and a second mode ofoutputting a scan line selection signal at a frequency of more than orequal to 11.6 μHz (once per day) and less than 0.1 Hz (0.1 times persecond), preferably more than or equal to 0.28 mHz (once per hour) andless than 1 Hz (once per second).

<<Synchronization Signal Supply Portion>>

The synchronization signal supply portion 212 supplies, in accordancewith the supplied synchronization control signal SC, a firstsynchronization signal SYNC(1) and a second synchronization signalSYNC(2) that make the driver circuits each supply scan line selectionsignals at different frequencies.

For example, the synchronization signal supply portion 212 controls theoutput frequency of a start pulse signal supplied to the scan linedriver circuit, whereby scan line selection signals can be supplied atdifferent frequencies.

<<Control Portion>>

A control portion 210D supplies a synchronization control signal SC tothe synchronization signal supply portion 212 and makes the drivercircuit supply scan line selection signals at different frequencies. Forexample, when a moving image is displayed, the control portion 210Dsupplies a synchronization control signal SC for supplying scan lineselection signals at a high frequency, and when a still image isdisplayed, the control portion 210D supplies a synchronization controlsignal SC for supplying scan line selection signals at a low frequency.

<<Transistor>>

The second transistor 634 t_2 supplies a current corresponding to thepotential of the signal line S to control the light emission of the ELelement 635EL.

As an example of a transistor that can be suitably used as the firsttransistor 634 t_1 or the second transistor 634 t_2, a transistorincluding an oxide semiconductor can be given.

A transistor including an oxide semiconductor film can have leakagecurrent between a source and a drain in an off state (off-state current)much lower than that of a conventional transistor including silicon.

When a transistor with extremely low off-state current is used in apixel portion of a display portion, frame frequency can be lowered whileflicker is reduced.

Furthermore, in the processing 2 in this embodiment, pixels in thesecond region 230(2) in each of which a transistor with extremely lowoff-state current including an oxide semiconductor is used can holdimage signals for a black image supplied to the second region 230(2) fora long time, as compared to the case where a transistor includingsilicon is used. Thus, the display in a region where display becomesunnecessary can be stopped. Consequently, a display device with lowpower consumption can be provided. Furthermore, a display device inwhich an image is displayed in a region that can be used in a foldedstate can be provided.

An example of a structure of the transistor that can be suitably used asthe first transistor 634 t_1 or the second transistor 634 t_2 isdescribed in Embodiment 4.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 3

In this embodiment, a structure of a display device 200C of oneembodiment of the present invention is described with reference to FIGS.7A to 7C, FIGS. 8A to 8D, and FIGS. 9A and 9B.

FIGS. 7A to 7C are perspective views illustrating the structure of thedisplay device 200C of one embodiment of the present invention. FIG. 7Aillustrates the display device 200C in an opened state. FIG. 7Billustrates the display device 200C in a bent state, and FIG. 7Cillustrates the display device 200C in a folded state.

FIGS. 8A to 8D illustrate the structure of the display device 200C ofone embodiment of the present invention. FIG. 8A is a top view of thedisplay device 200C that is opened, and FIG. 8B is a bottom view of thedisplay device 200C that is opened. FIG. 8C is a side view of thedisplay device 200C that is opened, and FIG. 8D is a cross-sectionalview taken alone dashed-dotted line A-B in FIG. 8A.

FIGS. 9A and 9B illustrate the structure of a display panel of thedisplay device 200C of one embodiment of the present invention. FIG. 9Ais a cross-sectional view of the center of the display device 200C in afolded state, and FIG. 9B is a top view of the display panel in anopened state.

The display device 200C described in this embodiment includes a foldabledisplay portion including the first region 230(1) and the second region230(2); driver circuits that drive the display portion; an imageprocessing portion that supplies an image signal to the driver circuits;the sensing portion 240 that senses an opened state or a folded state ofthe display portion and supplies a fold signal; and a control portionthat receives the fold signal (FIG. 7A).

The control portion supplies an image control signal in accordance withthe fold signal, and the image processing portion generates, inaccordance with the image control signal, an image in which a blackimage is displayed in the second region 230(2).

Note that the driver circuits, the image processing portion, and thecontrol portion are provided between support panels 15 a and supportpanels 15 b.

The display device 200C includes a strip-like high flexibility region E1and a strip-like low flexibility region E2 that are arrangedalternately, in other words, form stripes (FIG. 8A). Note that theregions are not necessarily arranged in parallel to each other.

A connecting member 13 a is partly exposed between two support panels 15a apart from each other. In addition, a connecting member 13 b is partlyexposed between two support panels 15 b apart from each other (FIGS. 8Aand 8B).

The display device 200C can be folded by bending the high flexibilityregion E1 (see FIGS. 7B and 7C).

<<High Flexibility Region>>

The high flexibility region E1 serves as a hinge. The high flexibilityregion E1 includes at least a flexible display panel.

The high flexibility region E1 includes the connecting member 13 a onthe image display side of the display panel and the connecting member 13b on the opposite side (see FIGS. 8A and 8B). The display panel is heldbetween the connecting member 13 a and the connecting member 13 b (seeFIG. 7A and FIGS. 8C and 8D).

<<Low Flexibility Region>>

The low flexibility region E2 includes the support panel 15 a on theimage display side of the display panel and the support panel 15 b onthe opposite side. The display panel is held between the support panel15 a and the support panel 15 b.

A stacked body in which the support panel 15 a and the support panel 15b overlap with each other has a lower flexibility than that of thedisplay panel.

The support panels 15 a and the support panels 15 b support the displaypanel to increase its mechanical strength and can prevent breakage ofthe display panel.

The scan line driver circuit 232G(1), the scan line driver circuit232G(2), and the signal line driver circuit 232S(1) are held between thesupport panels 15 a and the support panels 15 b. Thus, the drivercircuits can be protected from external stress (see FIGS. 9A and 9B).

Note that the support panels may be placed on only one of the displaysurface side and the side opposite to the display surface side of thedisplay panel. For example, a display device that includes the pluralityof support panels 15 b and does not include the plurality of supportpanels 15 a may be employed. Thus, the display device can be made thinand/or lightweight.

<<Connecting Member and Support Panel>>

For the connecting member 13 a, the connecting member 13 b, the supportpanels 15 a, and the support panels 15 b, for example, plastic, a metal,an alloy, and/or rubber can be used.

Plastic, rubber, or the like is preferably used because it can form aconnecting member or a support panel that is lightweight and less likelyto be broken. For example, silicone rubber may be used for theconnecting member and stainless steel or aluminum may be used for thesupport panel.

In the case where a connecting member or a support panel is placed onthe display surface side of the display panel, a light-transmittingmaterial is used for a portion that overlaps with a region where displayis performed on the display panel, i.e., the first region 230(1) and thesecond region 230(2).

To fix two of the connecting member, the support panel, and the displaypanel, for example, an adhesive, a screw or pin that penetrates them, ora clip that holds them can be used.

<<Sensing Portion and Sign>>

The sign 239 and the sensing portion 240 are provided on the supportpanels 15 a to sense an opened state or a folded state of the displayportion 230 (see FIGS. 7A and 7B and FIGS. 8A and 8C).

When the display portion 230 is in an opened state, the sign 239 is awayfrom the sensing portion 240 (see FIG. 7A).

When the display portion 230 is bent at the connecting member 13 a, thesign 239 gets close to the sensing portion 240 (see FIG. 7B).

When the display portion 230 is folded at the connecting member 13 a,the sign 239 faces the sensing portion 240 (see FIG. 7C). The sensingportion 240 senses the sign 239 facing it, recognizes a folded state,and supplies a fold signal F indicating a folded state.

<<Display Panel>>

The display panel includes the display portion, first driver circuits,and second driver circuits (see FIGS. 9A and 9B).

The display portion includes the first region 230(1) and the secondregion 230(2).

The first driver circuits include the scan line driver circuit 232G(1)and the signal line driver circuit 232S(1). The second driver circuitsinclude the scan line driver circuit 232G(2), a signal line drivercircuit 232S(2 a), and a signal line driver circuit 232S(2 b).

The first driver circuits drive the first region 230(1). The seconddriver circuits drive the second region 230(2). The signal line drivercircuit 232S(2 a) and the signal line driver circuit 232S(2 b) supplyimage signals to pixels to which the scan line driver circuit 232G(2)supplies a selection signal.

There is the boundary 230 b(1) between the first region 230(1) and thesecond region 230(2). In addition, there is a region 230(1)S that isclose to the boundary 230 b(1) and is in the first region 230(1) (seeFIG. 9B). The region 230(1)S is on a side surface of the display device200C in a folded state (see FIG. 9A).

The first region 230(1) includes the region 230(1)S. Even when drivingof the second region 230(2) of the display device 200C is stopped in afolded state, an image can be displayed in the region 230(1)S by drivingthe first region 230(1). In this manner, an image can be displayed onthe side surface of the display device 200C; thus, the side surface canbe effectively utilized.

Structures of the flexible display panel are described in Embodiments 6and 7.

The display device 200C in a folded state is highly portable. It ispossible to fold the display device 200C such that the first region230(1) of the display portion is on the outer side and use only thefirst region 230(1) for display (see FIG. 7C). For example, when thedisplay portion is provided with a touch panel and has a size such thatit can be supported with one hand in a folded state, the touch panel canbe operated with the thumb of the hand supporting it. Thus, a displaydevice that can be operated with one hand in a folded state can beprovided.

When the second region 230(2) that is hidden from a user in a foldedstate is not driven in a folded state, the power consumption of thedisplay device 200C can be reduced. Moreover, folding the display device200C such that the second region 230(2) is on the inner side can preventdamage and attachment of dirt to the second region 230(2).

The display device 200C can display an image on a seamless large regionin an opened state. Thus, highly browsable display is possible.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 4

In this embodiment, a structure of a transistor 151 that can be used ina display device of one embodiment of the present invention is describedwith reference to FIGS. 10A to 10C.

FIGS. 10A to 10C are a top view and cross-sectional views of thetransistor 151. FIG. 10A is a top view of the transistor 151, FIG. 10Bis a cross-sectional view taken along dashed-dotted line A-B in FIG.10A, and FIG. 10C is a cross-sectional view taken along dashed-dottedline C-D in FIG. 10A. Note that in FIG. 10A, some components are notillustrated for clarity.

Note that in this embodiment, the first electrode refers to one of asource and a drain of a transistor, and the second electrode refers tothe other.

The transistor 151 is a channel-etched transistor and includes a gateelectrode 104 a provided over a substrate 102, a first insulating film108 that includes insulating films 106 and 107 and is formed over thesubstrate 102 and the gate electrode 104 a, an oxide semiconductor film110 overlapping with the gate electrode 104 a with the first insulatingfilm 108 provided therebetween, and a first electrode 112 a and a secondelectrode 112 b in contact with the oxide semiconductor film 110. Inaddition, over the first insulating film 108, the oxide semiconductorfilm 110, the first electrode 112 a, and the second electrode 112 b, asecond insulating film 120 including insulating films 114, 116, and 118and a gate electrode 122 c formed over the second insulating film 120are provided. The gate electrode 122 c is connected to the gateelectrode 104 a in openings 142 d and 142 e provided in the firstinsulating film 108 and the second insulating film 120. In addition, aconductive film 122 a serving as a pixel electrode is formed over theinsulating film 118. The conductive film 122 a is connected to thesecond electrode 112 b through an opening 142 a provided in the secondinsulating film 120.

Note that the first insulating film 108 serves as a first gateinsulating film of the transistor 151, and the second insulating film120 serves as a second gate insulating film of the transistor 151.Furthermore, the conductive film 122 a serves as a pixel electrode.

In the channel width direction of the transistor 151 of one embodimentof the present invention, the oxide semiconductor film 110 is providedbetween the gate electrode 104 a and the gate electrode 122 c with thefirst insulating film 108 provided between the gate electrode 104 a andthe oxide semiconductor film 110 and with the second insulating film 120provided between the gate electrode 122 c and the oxide semiconductorfilm 110. In addition, as illustrated in FIG. 10A, the gate electrode104 a overlaps with side surfaces of the oxide semiconductor film 110with the first insulating film 108 provided therebetween, when seen fromthe above.

A plurality of openings is provided in the first insulating film 108 andthe second insulating film 120. Typically, as illustrated in FIG. 10B,the opening 142 a through which part of the second electrode 112 b isexposed is provided. Furthermore, in the channel width direction, theopenings 142 d and 142 e are provided with the oxide semiconductor film110 provided therebetween as illustrated in FIG. 10C. In other words,the openings 142 d and 142 e are provided on outer sides of the sidesurfaces of the oxide semiconductor film 110.

In the opening 142 a, the second electrode 112 b is connected to theconductive film 122 a.

In addition, in the openings 142 d and 142 e, the gate electrode 104 ais connected to the gate electrode 122 c. This means that the gateelectrode 104 a and the gate electrode 122 c surround the oxidesemiconductor film 110 in the channel width direction with the firstinsulating film 108 and the second insulating film 120 provided betweenthe oxide semiconductor film 110 and each of the gate electrode 104 aand the gate electrode 122 c. Furthermore, the gate electrode 122 c onthe side surfaces of the openings 142 d and 142 e faces the sidesurfaces of the oxide semiconductor film 110.

The gate electrode 104 a and the gate electrode 122 c are included, thesame potential is applied to the gate electrode 104 a and the gateelectrode 122 c, the side surface of the oxide semiconductor film 110faces the gate electrode 122 c, and the gate electrode 104 a and thegate electrode 122 c surround the oxide semiconductor film 110 in thechannel width direction with the first insulating film 108 and thesecond insulating film 120 provided between the oxide semiconductor film110 and each of the gate electrode 104 a and the gate electrode 122 c;thus, carriers flow not only at the interfaces between the oxidesemiconductor film 110 and each of the first insulating film 108 and thesecond insulating film 120 but also in a wide region in the oxidesemiconductor film 110, which results in an increase in the amount ofcarriers that move in the transistor 151.

As a result, the on-state current of the transistor 151 is increased,and the field-effect mobility is increased to greater than or equal to10 cm²/V·s or to greater than or equal to 20 cm²/V·s, for example. Notethat here, the field-effect mobility is not an approximate value of themobility as the physical property of the oxide semiconductor film but isthe apparent field-effect mobility in a saturation region of thetransistor, which is an indicator of current drive capability. Note thatan increase in field-effect mobility becomes significant when thechannel length (also referred to as L length) of the transistor islonger than or equal to 0.5 μm and shorter than or equal to 6.5 μm,preferably longer than 1 μm and shorter than 6 μm, further preferablylonger than 1 μm and shorter than or equal to 4 μm, still furtherpreferably longer than 1 μm and shorter than or equal to 3.5 μm, yetstill further preferably longer than 1 μm and shorter than or equal to2.5 μm. Furthermore, with a short channel length longer than or equal to0.5 μm and shorter than or equal to 6.5 μm, the channel width can alsobe short.

Thus, even if a plurality of regions to be connection portions betweenthe gate electrode 104 a and the gate electrode 122 c is provided, thearea of the transistor 151 can be reduced.

Defects are formed at the end portion of the oxide semiconductor film110, which is processed by etching or the like, because of damage due tothe processing, and the end portion is polluted by attachment ofimpurities or the like. For this reason, in the case where only one ofthe gate electrode 104 a and the gate electrode 122 c is formed in thetransistor 151, even when the oxide semiconductor film 110 is intrinsicor substantially intrinsic, the end portion of the oxide semiconductorfilm 110 is easily activated to be an n-type region (a low-resistanceregion) by application of stress such as an electric field.

In the case where the n-type end portions overlap with regions betweenthe first electrode 112 a and the second electrode 112 b, the n-typeregions serve as carrier paths, resulting in formation of a parasiticchannel. As a result, drain current with respect to the thresholdvoltage is gradually increased, so that the threshold voltage of thetransistor shifts in the negative direction. However, as illustrated inFIG. 10C, the gate electrode 104 a and the gate electrode 122 c havingthe same potentials are included and the gate electrode 122 c faces theside surfaces of the oxide semiconductor film 110 in the channel widthdirection at the side surfaces of the second insulating film 120,whereby an electric field from the gate electrode 122 c affects theoxide semiconductor film 110 also from the side surfaces of the oxidesemiconductor film 110. As a result, a parasitic channel is preventedfrom being generated at the side surface of the oxide semiconductor film110 or the end portion including the side surface and its vicinity.Thus, the transistor having favorable electrical characteristics of asharp increase in drain current with respect to the threshold voltage isobtained.

The transistor includes the gate electrode 104 a and the gate electrode122 c, each of which has a function of blocking an external electricfield; thus, charges such as a charged particle between the substrate102 and the gate electrode 104 a and over the gate electrode 122 c donot affect the oxide semiconductor film 110. Thus, degradation due to astress test e.g., a negative gate bias temperature (−GBT) stress test inwhich a negative potential is applied to a gate electrode) can bereduced, and changes in the rising voltages of on-state current atdifferent drain voltages can be suppressed.

The BT stress test is one kind of accelerated test and can evaluate, ina short time, change in characteristics (i.e., a change over time) oftransistors, which is caused by long-term use. In particular, the amountof change in threshold voltage of a transistor between before and afterthe BT stress test is an important indicator when examining thereliability of the transistor. If the amount of change in the thresholdvoltage between before and after the BT stress test is small, thetransistor has higher reliability.

Elements included in the transistor 151 are described below.

<<Substrate 102>>

For the substrate 102, a glass material such as aluminosilicate glass,aluminoborosilicate glass, or barium borosilicate glass is used, in themass production, for the substrate 102, a mother glass with any of thefollowing sizes is preferably used: the 8-th generation (2160 mm×2460mm), the 9-th generation (2400 mm×2800 mm or 2450 mm×3050 mm), the 10-thgeneration (2950 mm×3400 mm), and the like. High process temperature anda long period of process time drastically shrink the mother glass. Thus,in the case where mass production is performed with the use of themother glass, it is preferable that the heat process in themanufacturing process be performed at a temperature lower than or equalto 600° C., preferably lower than or equal to 450° C., furtherpreferably lower than or equal to 350° C.

<<Gate Electrode 104 a>>

As a material used for the gate electrode 104 a, a metal elementselected from aluminum, chromium, copper, tantalum, titanium,molybdenum, and tungsten, an alloy containing any of these metalelements as a component, an alloy containing these metal elements incombination, or the like can be used. The gate electrode 104 a may havea single-layer structure or a stacked-layer structure of two or morelayers. For example, a two-layer structure in which a titanium film isstacked over an aluminum film, a two-layer structure in which a titaniumfilm is stacked over a titanium nitride film, a two-layer structure inwhich a tungsten film is stacked over a titanium nitride film, atwo-layer structure in which a tungsten film is stacked over a tantalumnitride film or a tungsten nitride film, a three-layer structure inwhich a titanium film, an aluminum film, and a titanium film are stackedin this order, and the like can be given. Alternatively, a film, analloy film, or a nitride film which contains aluminum and one or moreelements selected from titanium, tantalum, tungsten, molybdenum,chromium, neodymium, and scandium may be used. The gate electrode 104 acan be formed by a sputtering method, for example.

<<First Insulating Film>>

An example in which the first insulating film 108 has a two-layerstructure of the insulating film 106 and the insulating film 107 isillustrated. Note that the structure of the first insulating film 108 isnot limited thereto, arid for example, the first insulating film 108 mayhave a single-layer structure or a stacked-layer structure includingthree or more layers.

The insulating film 106 is formed with a single-layer structure or astacked-layer structure using, for example, any of a silicon nitrideoxide film, a silicon nitride film, an aluminum oxide film, and the likewith a PE-CVD apparatus. In the case where the insulating film 106 has astacked-layer structure, it is preferable that a silicon nitride filmwith fewer defects be provided as a first silicon nitride film, and asilicon nitride film from which hydrogen and ammonia are less likely tobe released be provided over the first silicon nitride film, as a secondsilicon nitride film. As a result, hydrogen and nitrogen contained inthe insulating film 106 can be inhibited from moving or diffusing intothe oxide semiconductor film 110 to be formed later.

The insulating film 107 is formed with a single-layer structure or astacked-layer structure using any of a silicon oxide film, a siliconoxynitride film, and the like with a PE-CVD apparatus.

The first insulating film 108 can have a stacked-layer structure, forexample, in which a 400-nm-thick silicon nitride film used as theinsulating film 106 and a 50-nm-thick silicon oxynitride film used asthe insulating film 107 are formed in this order. The silicon nitridefilm and the silicon oxynitride film are preferably formed in successionin a vacuum, in which case entry of impurities is suppressed. The firstinsulating film 108 in a position overlapping with the gate electrode104 a serves as gate insulating film of the transistor 151. Note thatsilicon nitride oxide refers to an insulating material that containsmore nitrogen than oxygen, whereas silicon oxynitride refers to aninsulating material that contains more oxygen than nitrogen.

<<Oxide Semiconductor Film 110>>

The oxide semiconductor film 110 preferably includes a film representedby an In-M-Zn oxide that contains at least indium (In), zinc (Zn), and M(M is a metal such as Al, Ga, Ge, Y, Zr, Sn, La, Ce, or Hf).Alternatively, both In and Zn are preferably contained. In order toreduce fluctuations in electrical characteristics of the transistorsincluding the oxide semiconductor, the oxide semiconductor preferablycontains a stabilizer in addition to In and Zn.

As a stabilizer, gallium (Ga), tin (Sn), hafnium (Hf), aluminum (Al),zirconium (Zr), and the like can be given. As another stabilizer,lanthanoid such as lanthanum (La), cerium (Ce), praseodymium (Pr),neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), or lutetium (Lu) can be given.

As the oxide semiconductor included in the oxide semiconductor film 110,any of the following can be used: an In-Ga-Zn-based oxide, anIn-Al-Zn-based oxide, an In-Sn-Zn-based oxide, an In-Hf-Zn-based oxide,an In-La-Zn-based oxide, an In-Ce-Zn-based oxide, an In-Pr-Zn-basedoxide, an In-Nd-Zn-based oxide, an In-Sm-Zn-based oxide, anIn-Eu-Zn-based oxide, an In-Gd-Zn-based oxide, an In-Tb-Zn-based oxide,an In-Dy-Zn-based oxide, an In-Ho-Zn-based oxide, an In-Er-Zn-basedoxide, an In-Tm-Zn-based oxide, an In-Yb-Zn-based oxide, anIn-Lu-Zn-based oxide, an In-Sn-Ga-Zn-based oxide, an In-Hf-Ga-Zn-basedoxide, an In-Al-Ga-Zn-based oxide, an In-Sn-Al-Zn-based oxide, anIn-Sn-Hf-Zn-based oxide, and an In-Hf-Al-Zn-based oxide.

Note that here, for example, an “In-Ga-Zn-based oxide” means an oxidecontaining In, Ga, and Zn as its main components and there is nolimitation on the ratio of In:Ga:Zn. The In-Ga-Zn-based oxide maycontain another metal element in addition to In, Ga, and Zn.

The oxide semiconductor film 110 can be formed by a sputtering method, amolecular beam epitaxy (MBE) method, a CVD method, a pulse laserdeposition method, an atomic layer deposition (ALD) method, or the likeas appropriate. In particular, the oxide semiconductor film 110 ispreferably formed by the sputtering method because the oxidesemiconductor film 110 can be dense.

In the formation of an oxide semiconductor film as the oxidesemiconductor film 110, the hydrogen concentration in the oxidesemiconductor film is preferably reduced as much as possible. To reducethe hydrogen concentration, for example, in the case of a sputteringmethod, a deposition chamber needs to be highly evacuated and also asputtering gas needs to be highly purified. As an oxygen gas or an argongas used for a sputtering gas, a gas which is highly purified to have adew point of −40° C. or lower, preferably −80° C. or lower, furtherpreferably −100° C. or lower, or still further preferably −120° C. orlower is used, whereby entry of moisture or the like into the oxidesemiconductor film can be minimized.

In order to remove moisture remaining in the deposition chamber, anentrapment vacuum pump, such as a cryopump, an ion pump, or a titaniumsublimation pump, is preferably used. A turbo molecular pump providedwith a cold trap may be alternatively used. When the deposition chamberis evacuated with a cryopump, which has a high capability in removing ahydrogen molecule, a compound including a hydrogen atom such as water(H₂O), a compound including a carbon atom, and the like, theconcentration of an impurity to be contained in a film formed in thedeposition chamber can be reduced.

When the oxide semiconductor film as the oxide semiconductor film 110 isformed by a sputtering method, the relative density (filling factor) ofa metal oxide target that is used for the film formation is greater thanor equal to 90% and less than or equal to 100%, preferably greater thanor equal to 95% and less than or equal to 100%. With the use of themetal oxide target having high relative density, a dense oxidesemiconductor film can be formed.

Note that to reduce the impurity concentration of the oxidesemiconductor film, it is also effective to form the oxide semiconductorfilm as the oxide semiconductor film 110 while the substrate 102 is keptat high temperature. The heating temperature of the substrate 102 may behigher than or equal to 150° C. and lower than or equal to 450° C., andpreferably the substrate temperature is higher than or equal to 200° C.and lower than or equal to 350° C.

Next, first heat treatment is preferably performed. The first heattreatment may be performed at a temperature higher than or equal to 250°C. and lower than or equal to 650° C., preferably higher than or equalto 300° C. and lower than or equal to 500° C., in an inert gasatmosphere, an atmosphere containing an oxidizing gas at 10 ppm or more,or a reduced pressure state. Alternatively, the first heat treatment maybe performed in such a manner that heat treatment is performed in aninert gas atmosphere, and then another heat treatment is performed in anatmosphere containing an oxidizing gas at 10 ppm or more, in order tocompensate for desorbed oxygen. By the first heat treatment, thecrystallinity of the oxide semiconductor that is used as the oxidesemiconductor film 110 can be improved, and in addition, impurities suchas hydrogen and water can be removed from the first insulating film 108and the oxide semiconductor film 110. The first heat treatment may beperformed before the oxide semiconductor film 110 is processed into anisland shape.

<<First Electrode and Second Electrode>>

The first electrode 112 a and the second electrode 112 b can be formedusing a conductive film 112 having a single-layer structure or astacked-layer structure with any of metals such as aluminum, titanium,chromium, nickel, copper, yttrium, zirconium, molybdenum, silver,tantalum, and tungsten, or an alloy containing any of these metals asits main component. In particular, one or more elements selected fromaluminum, chromium, copper, tantalum, titanium, molybdenum, and tungstenare preferably included. For example, a two-layer structure in which atitanium film is stacked over an aluminum film, a two-layer structure inwhich a titanium film is stacked over a tungsten film, a two-layerstructure in which a copper film is formed over acopper-magnesium-aluminum alloy film, a three-layer structure in which atitanium film or a titanium nitride film, an aluminum film or a copperfilm, and a titanium film or a titanium nitride film are stacked in thisorder, a three-layer structure in which a molybdenum film or amolybdenum nitride film, an aluminum film or a copper film, and amolybdenum film or a molybdenum nitride film are stacked in this order,and the like can be given. Note that a transparent conductive materialcontaining indium oxide, tin oxide, or zinc oxide may be used. Theconductive film can be formed by a sputtering method, for example.<<Insulating Films 114, 116, and 118>>

An example in which the second insulating film 120 has a three-layerstructure of the insulating films 114, 116, and 118 is illustrated. Notethat the structure of the second insulating film 120 is not limitedthereto, and for example, the second insulating film 120 may have asingle-layer structure or a stacked-layer structure including two layersor four or more layers.

For the insulating films 114 and 116, an inorganic insulating materialcontaining oxygen can be used in order to improve the characteristics ofthe interface with the oxide semiconductor used for the oxidesemiconductor film 110. As examples of the inorganic insulating materialcontaining oxygen, a silicon oxide film, a silicon oxynitride film, andthe like can be given. The insulating films 114 and 116 can be formed bya PE-CVD method, for example.

The thickness of the insulating film 114 can be greater than or equal to5 nm and less than or equal to 150 nm, preferably greater than or equalto 5 nm and less than or equal to 50 nm, more preferably greater than orequal to 10 nm and less than or equal to 30 nm. The thickness of theinsulating film 116 can be greater than or equal to 30 nm and less thanor equal to 500 nm, preferably greater than or equal to 150 nm and lessthan or equal to 400 nm.

Further, the insulating films 114 and 116 can be formed using insulatingfilms formed of the same kinds of materials; thus, a boundary betweenthe insulating films 114 and 116 cannot be clearly observed in somecases. Thus, in this embodiment, the boundary between the insulatingfilms 114 and 116 is shown by a dashed line. Although a two-layerstructure of the insulating films 114 and 116 is described in thisembodiment, the present invention is not limited to this. For example, asingle-layer structure of the insulating film 114, a single-layerstructure of the insulating film 116, or a stacked-layer structureincluding three or more layers may be used.

The insulating film 118 is a film formed using a material that canprevent an external impurity, such as water, alkali metal, or alkalineearth metal, from diffusing into the oxide semiconductor film 110, andthat further contains hydrogen.

For example, a silicon nitride film, a silicon nitride oxide film, orthe like having a thickness of greater than or equal to 150 nm and lessthan or equal to 400 nm can be used as the insulating film 118. In thisembodiment, a 150-nm-thick silicon nitride film is used as theinsulating film 118.

The silicon nitride film is preferably formed at a high temperature tohave an improved blocking property against impurities or the like; forexample, the silicon nitride film is preferably formed at a temperaturein the range from the substrate temperature of 100° C. to the strainpoint of the substrate, more preferably at a temperature in the rangefrom 300° C. to 400° C. When the silicon nitride film is formed at ahigh temperature, a phenomenon in which oxygen is released from theoxide semiconductor used for the oxide semiconductor film 110 and thecarrier concentration is increased is caused in some cases; therefore,the upper limit of the temperature is a temperature at which thephenomenon is not caused.

<<Conductive Film 122 a and Gate Electrode 122 c>>

For the conductive film used as the conductive film 122 a and the gateelectrode 122 c, an oxide containing indium may be used. For example, alight-transmitting conductive material such as indium oxide containingtungsten oxide, indium zinc oxide containing tungsten oxide, indiumoxide containing titanium oxide, indium tin oxide containing titaniumoxide, indium tin oxide (hereinafter referred to as ITO), indium zincoxide, or indium tin oxide to which silicon oxide is added can be used.The conductive film that can be used as the conductive film 122 a andthe gate electrode 122 c can be formed by a sputtering method, forexample.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 5

In this embodiment, an example of an oxide semiconductor film that canbe used in the transistor 151 in Embodiment 4 is described.

<Crystallinity of Oxide Semiconductor Film>

A structure of the oxide semiconductor film is described below.

An oxide semiconductor film is classified roughly into a single-crystaloxide semiconductor film and a non-single-crystal oxide semiconductorfilm. The non-single-crystal oxide semiconductor film includes any of ac-axis aligned crystalline oxide semiconductor (CAAC-OS) film, apolycrystalline oxide semiconductor film, a microcrystalline oxidesemiconductor film, an amorphous oxide semiconductor film, and the like.

First, a CAAC-OS film is described.

The CAAC-OS film is one of oxide semiconductor films including aplurality of crystal parts, and most of the crystal parts each fitinside a cube whose one side is less than 100 nm. Thus, there is a casewhere a crystal part included in the CAAC-OS film fits inside a cubewhose one side is less than 10 nm, less than 5 nm, or less than 3 nm.

In a transmission electron microscope (TEM) image of the CAAC-OS film, aboundary between crystal parts, that is, a grain boundary is not clearlyobserved. Thus, in the CAAC-OS film, a reduction in electron mobilitydue to the grain boundary is less likely to occur.

According to the TEM image of the CAAC-OS film observed in a directionsubstantially parallel to a sample surface (cross-sectional TEM image),metal atoms are arranged in a layered manner in the crystal parts. Eachmetal atom layer has a morphology reflected by a surface over which theCAAC-OS film is formed (hereinafter, a surface over which the CAAC-OSfilm is formed is referred to as a formation surface) or a top surfaceof the CAAC-OS film, and is arranged in parallel to the formationsurface or the top surface of the CAAC-OS film.

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 10°, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 5°.The term “perpendicular” indicates that the angle formed between twostraight lines is greater than or equal to 80° and less than or equal to100°, and accordingly includes the case where the angle is greater thanor equal to 85° and less than or equal to 95°.

On the other hand, according to the TEM image of the CAAC-OS filmobserved in a direction substantially perpendicular to the samplesurface (plan TEM image), metal atoms are arranged in a triangular orhexagonal configuration in the crystal parts. However, there is noregularity of arrangement of metal atoms between different crystalparts.

From the results of the cross-sectional TEM image and the plan TEMimage, alignment is found in the crystal parts in the CAAC-OS film.

A CAAC-OS film is subjected to structural analysis with an X-raydiffraction (XRD) apparatus, For example, when the CAAC-OS filmincluding an InGaZnO₄ crystal is analyzed by an out-of-plane method, apeak appears frequently when the diffraction angle (2θ) is around 31°.This peak is derived from the (009) plane of the InGaZnO₄ crystal, whichindicates that crystals in the CAAC-OS film have c-axis alignment, andthat the c-axes are aligned in a direction substantially perpendicularto the formation surface or the top surface of the CAAC-OS film.

On the other hand, when the CAAC-OS film is analyzed by an in-planemethod in which an X-ray enters a sample in a direction substantiallyperpendicular to the c-axis, a peak appears frequently when 2θ is around56°. This peak is derived from the (110) plane of the InGaZnO₄ crystal.Here, analysis (ϕ scan) is performed under conditions where the sampleis rotated around a normal vector of a sample surface as an axis (ϕaxis) with 2θ fixed at around 56°. In the case where the sample is asingle-crystal oxide semiconductor film of InGaZnO₄, six peaks appear.The six peaks are derived from crystal planes equivalent to the (110)plane. On the other hand, in the case of a CAAC-OS film, a peak is notclearly observed even when ϕ scan is performed with 2θ fixed at around56°.

According to the above results, in the CAAC-OS film having c-axisalignment, while the directions of a-axes and b-axes are differentbetween crystal parts, the c-axes are aligned in a direction parallel toa normal vector of a formation surface or a normal vector of a topsurface. Thus, each metal atom layer arranged in a layered mannerobserved in the cross-sectional TEM image corresponds to a planeparallel to the a-b plane of the crystal.

Note that the crystal part is formed concurrently with deposition of theCAAC-OS film or is formed through crystallization treatment such as heattreatment. As described above, the c-axis of the crystal is aligned in adirection parallel to a normal vector of a formation surface or a normalvector of a top surface. Thus, for example, in the case where a shape ofthe CAAC-OS film is changed by etching or the like, the c-axis might notbe necessarily parallel to a normal vector of a formation surface or anormal vector of a top surface of the CAAC-OS film.

Further, the degree of crystallinity in the CAAC-OS film is notnecessarily uniform. For example, in the case where crystal growthleading to the CAAC-OS film occurs from the vicinity of the top surfaceof the film, the degree of the crystallinity in the vicinity of the topsurface is higher than that in the vicinity of the formation surface insome cases. Further, when an impurity is added to the CAAC-OS film, thecrystallinity in a region to which the impurity is added is changed, andthe degree of crystallinity in the CAAC-OS film varies depending onregions.

Note that when the CAAC-OS film with an InGaZnO₄ crystal is analyzed byan out-of-plane method, a peak of 2θ may also be observed at around 36°,in addition to the peak of 2θ at around 31°. The peak of 2θ at around36° indicates that a crystal having no c-axis alignment is included inpart of the CAAC-OS film. It is preferable that in the CAAC-OS film, apeak of 2θ appear at around 31° and a peak of 2θ do not appear at around36°.

In this specification, trigonal and rhombohedral crystal systems areincluded in a hexagonal crystal system.

The CAAC-OS film is an oxide semiconductor film having a low impurityconcentration. The impurity is an element other than the main componentsof the oxide semiconductor film, such as hydrogen, carbon, silicon, or atransition metal element. In particular, an element that has higherbonding strength to oxygen than a metal element included in the oxidesemiconductor film, such as silicon, disturbs the atomic arrangement ofthe oxide semiconductor film by depriving the oxide semiconductor filmof oxygen and causes a decrease in crystallinity. Further, a heavy metalsuch as iron or nickel, argon, carbon dioxide, or the like has a largeatomic radius (molecular radius), and thus disturbs the atomicarrangement of the oxide semiconductor film and causes a decrease incrystallinity when it is contained in the oxide semiconductor film. Notethat the impurity contained in the oxide semiconductor film might serveas a carrier trap or a carrier generation source.

The CAAC-OS film is an oxide semiconductor film having a low density ofdefect states.

With the use of the CAAC-OS film in a transistor, variation in theelectrical characteristics of the transistor due to irradiation withvisible light or ultraviolet light is small.

Next, a microcrystalline oxide semiconductor film is described.

In an image obtained with the TEM, crystal parts cannot be found clearlyin the microcrystalline oxide semiconductor film in some cases. In mostcases, the size of a crystal part in the microcrystalline oxidesemiconductor film is greater than or equal to 1 nm and less than orequal to 100 nm, or greater than or equal to 1 nm and less than or equalto 10 nm. A microcrystal with a size greater than or equal to 1 nm andless than or equal to 10 nm, or a size greater than or equal to 1 nm andless than or equal to 3 nm is specifically referred to as nanocrystal(nc). An oxide semiconductor film including nanocrystal is referred toas a nanocrystalline oxide semiconductor (nc-OS) film. In an imageobtained with TEM, a grain boundary cannot be found clearly in the nc-OSfilm in some cases.

In the nc-OS film, a microscopic region (for example, a region with asize greater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic order. Note that there isno regularity of crystal orientation between different crystal parts inthe nc-OS film. Thus, the orientation of the whole film is not observed.Accordingly, in sonic cases, the nc-OS film cannot be distinguished froman amorphous oxide semiconductor film depending on an analysis method.For example, when the nc-OS film is subjected to structural analysis byan out-of-plane method with an XRD apparatus using an X-ray having adiameter larger than that of a crystal part, a peak which shows acrystal plane does not appear. Furthermore, a halo pattern is shown inan electron diffraction pattern (also referred to as a selected-areaelectron diffraction pattern) of the nc-OS film obtained by using anelectron beam having a probe diameter (e.g., greater than or equal to 50nm) larger than the diameter of a crystal part. Meanwhile, spots areshown in a nanobeam electron diffraction pattern of the nc-OS filmobtained by using an electron beam having a probe diameter (e.g.,greater than or equal to 1 nm and smaller than or equal to 30 nm) closeto, or smaller than or equal to a diameter of a crystal part. Further,in a nanobeam electron diffraction pattern of the nc-OS film, regionswith high luminance in a circular (ring) pattern are observed in somecases. Also in a nanobeam electron diffraction pattern of the nc-OSfilm, a plurality of spots are shown in a ring-like region in somecases.

The nc-OS film is an oxide semiconductor film that has high regularityas compared to an amorphous oxide semiconductor film. Therefore, thenc-OS film has a lower density of defect states than an amorphous oxidesemiconductor film. Note that there is no regularity of crystalorientation between different crystal parts in the nc-OS film.Therefore, the nc-OS film has a higher density of defect states than theCAAC-OS film.

Note that an oxide semiconductor film may be a stacked film includingtwo or more kinds of an amorphous oxide semiconductor film, amicrocrystalline oxide semiconductor film, and a CAAC-OS film, forexample.

<Method for Forming CAAC-OS Film>

For example, a CAAC-OS film is deposited by a sputtering method using apolycrystalline oxide semiconductor sputtering target. When ions collidewith the sputtering target, a crystal region included in the sputteringtarget may be separated from the target along an a-b plane; in otherwords, a sputtered particle having a plane parallel to an a-b plane(flat-plate-like sputtered particle or pellet-like sputtered particle)may flake off from the sputtering target. In that case, theflat-plate-like or pellet-like sputtered particle reaches a substratewhile maintaining its crystal state, whereby the CAAC-OS film can beformed.

The flat-plate-like or pellet-like sputtered particle has, for example,an equivalent circle diameter of a plane parallel to the a-b plane ofgreater than or equal to 3 nm and less than or equal to 10 nm, and athickness (length in the direction perpendicular to the a-b plane) ofgreater than or equal to 0.7 nm and less than 1 nm. Note that in theflat-plate-like or pellet-like sputtered particle, the plane parallel tothe a-b plane may be a regular triangle or a regular hexagon. Here, theterm “equivalent circle diameter of a plane” refers to the diameter of aperfect circle having the same area as the plane.

For the deposition of the CAAC-OS film, the following conditions arepreferably used.

By increasing the substrate temperature during the deposition, migrationof sputtered particles is likely to occur after the sputtered particlesreach a substrate surface. Specifically, the substrate temperatureduring the deposition is higher than or equal to 100° C. and lower thanor equal to 740° C., preferably higher than or equal to 200° C. andlower than or equal to 500° C. By increasing the substrate temperatureduring the deposition, when the flat-plate-like or pellet-like sputteredparticles reach the substrate, migration occurs on the substratesurface, so that a flat plane of the sputtered particles is attached tothe substrate. At this time, the sputtered particle is chargedpositively, whereby sputtered particles are attached to the substratewhile repelling each other; thus, the sputtered particles do not overlapwith each other randomly, and a CAAC-OS film with a uniform thicknesscan be deposited.

By reducing the amount of impurities entering the CAAC-OS film duringthe deposition, the crystal state can be prevented from being broken bythe impurities. For example, the concentration of impurities (e.g.,hydrogen, water, carbon dioxide, or nitrogen) which exist in thedeposition chamber may be reduced. Furthermore, the concentration ofimpurities in a deposition gas may be reduced. Specifically, adeposition gas whose dew point is −80° C. or lower, preferably −100° C.or lower is used.

Furthermore, it is preferable that the proportion of oxygen in thedeposition gas be increased and the power be optimized in order toreduce plasma damage at the deposition. The proportion of oxygen in thedeposition gas is higher than or equal to 30 vol %, preferably 100 vol%.

Alternatively, the CAAC-OS film is formed by the following method.

First, a first oxide semiconductor film is formed to a thickness ofgreater than or equal to 1 nm and less than 10 nm. The first oxidesemiconductor film is formed by a sputtering method. Specifically, thesubstrate temperature is set to higher than or equal to 100° C. andlower than or equal to 500° C., preferably higher than or equal to 150°C. and lower than or equal to 450° C., and the proportion of oxygen in adeposition gas is set to higher than or equal to 30 vol %, preferably100 vol %.

Next, heat treatment is performed so that the first oxide semiconductorfilm becomes a first CAAC-OS film with high crystallinity Thetemperature of the heat treatment is higher than or equal to 350° C. andlower than or equal to 740° C., preferably higher than or equal to 450°C. and lower than or equal to 650° C. The heat treatment time is longerthan or equal to 1 minute and shorter than or equal to 24 hours,preferably longer than or equal to 6 minutes and shorter than or equalto 4 hours. The heat treatment may be performed in an inert atmosphereor an oxidation atmosphere. It is preferable to perform heat treatmentin an inert atmosphere and then perform heat treatment in an oxidationatmosphere. The heat treatment in an inert atmosphere can reduce theconcentration of impurities in the first oxide semiconductor film in ashort time. At the same time, the heat treatment in an inert atmospheremay generate oxygen vacancies in the first oxide semiconductor film. Insuch a case, the heat treatment in an oxidation atmosphere can reducethe oxygen vacancies. Note that the heat treatment may be performedunder a reduced pressure, such as 1000 Pa or lower, 100 Pa or lower, 10Pa or lower, or 1 Pa or lower. The heat treatment under the reducedpressure can reduce the concentration of impurities in the first oxidesemiconductor film in a shorter time.

The first oxide semiconductor film with a thickness of greater than orequal to 1 nm and less than 10 nm can be easily crystallized by heattreatment as compared to the case where the first oxide semiconductorfilm has a thickness of greater than or equal to 10 nm.

Next, a second oxide semiconductor film having the same composition asthe first oxide semiconductor film is formed to a thickness of greaterthan or equal to 10 nm and less than or equal to 50 nm. The second oxidesemiconductor film is formed by a sputtering method. Specifically, thesubstrate temperature is set to higher than or equal to 100° C. andlower than or equal to 500° C., preferably higher than or equal to 150°C. and lower than or equal to 450° C., and the proportion of oxygen in adeposition gas is set to higher than or equal to 30 vol %, preferably100 vol %.

Next, heat treatment is performed so that solid phase growth of thesecond oxide semiconductor film is performed using the first CAAC-OSfilm, thereby forming a second CAAC-OS film with high crystallinity. Thetemperature of the heat treatment is higher than or equal to 350° C. andlower than or equal to 740° C., preferably higher than or equal to 450°C. and lower than or equal to 650° C. The heat treatment time is longerthan or equal to 1 minute and shorter than or equal to 24 hours,preferably longer than or equal to 6 minutes and shorter than or equalto 4 hours. The heat treatment may be performed in an inert atmosphereor an oxidation atmosphere, it is preferable to perform heat treatmentin an inert atmosphere and then perform heat treatment in an oxidationatmosphere. The heat treatment in an inert atmosphere can reduce theconcentration of impurities in the second oxide semiconductor film in ashort time. At the same time, the heat treatment in an inert atmospheremay generate oxygen vacancies in the second oxide semiconductor film. Insuch a case, the heat treatment in an oxidation atmosphere can reducethe oxygen vacancies. Note that the heat treatment may be performedunder a reduced pressure, such as 1000 Pa or lower, 100 Pa or lower, 10Pa or lower, or 1 Pa or lower. The heat treatment under the reducedpressure can reduce the concentration of impurities in the second oxidesemiconductor film in a shorter time.

In the above manner, a CAAC-OS film with a total thickness of greaterthan or equal to 10 nm can be formed. The CAAC-OS film can be favorablyused as the oxide semiconductor film in an oxide stack.

Next, a method for forming an oxide film in the case where a formationsurface has a low temperature because, for example, the substrate is notheated is described (for example, the temperature is lower than 130° C.,lower than 100° C., lower than 70° C. or at room temperatures (20° C. to25° C.)).

In the case where the formation surface has a low temperature, sputteredparticles fall irregularly to the formation surface. For example,migration does not occur; therefore, the sputtered particles arerandomly deposited on the formation surface including a region whereother sputtered particles have been deposited. That is, an oxide filmobtained by the deposition might have a non-uniform thickness and adisordered crystal alignment. The oxide film obtained in the abovemanner maintains the crystallinity of the sputtered particles to acertain degree and thus has a crystal part (nanocrystal).

For example, in the case where the pressure at the deposition is high,the frequency with which the flying sputtered particle collides withanother particle (e.g., an atom, a molecule, an ion, or a radical) ofargon or the like is increased. When the flying sputtered particlecollides with another particle (resputtered), the crystal structure ofthe sputtered particle might be broken. For example, when the sputteredparticle collides with another particle, the flat-plate-like orpellet-like shape of the sputtered particle cannot be kept, and thesputtered particle might be broken into parts (e.g., atomized). At thistime, when atoms obtained from the sputtered particle are deposited onthe formation surface, an amorphous oxide film might be formed.

In the case where not a sputtering method using a target including apolycrystalline oxide but a deposition method using liquid or a methodfor depositing a film by vaporizing a solid such as a target is used,the atoms separately fly to be deposited on the formation surface;therefore, an amorphous oxide film might be formed. Furthermore, forexample, by a laser ablation method, atoms, molecules, ions, radicals,clusters, or the like released from the target flies to be deposited onthe formation surface; therefore, an amorphous oxide film might beformed.

An oxide semiconductor film included in a resistor and a transistor inone embodiment of the present invention may have any of the abovecrystal states. Further, in the case of stacked oxide semiconductorfilms, the crystal states of the oxide semiconductor films may bedifferent from each other. Note that a CAAC-OS film is preferably usedas the oxide semiconductor film functioning as a channel of thetransistor. Further, the oxide semiconductor film included in theresistor has a higher impurity concentration than that of the oxidesemiconductor film included in the transistor; thus, the crystallinityis lowered in some cases.

The structures, the methods, and the like described in this embodimentcan be combined as appropriate with any of the structures, the methods,and the like described in the other embodiments.

Embodiment 6

In this embodiment, a structure of a display panel that can be used inthe display device of one embodiment of the present invention isdescribed with reference to FIGS. 11A to 11C. Note that the displaypanel described in this embodiment includes a touch sensor (a contactsensor device) that overlaps with a display portion; thus, the displaypanel can be called a touch panel (an input/output device).

FIG. 11A is a plan view illustrating the structure of a display panelthat can be used in the display device of one embodiment of the presentinvention.

FIG. 11B is a cross-sectional view taken along line A-E and line C-D inFIG. 11A.

FIG. 11C is a cross-sectional view taken along line E-F in FIG. 11A.

<Top View>

An input/output device 300 described as an example in this embodimentincludes a display portion 301 (see FIG. 11A).

The display portion 301 includes a plurality of pixels 302 and aplurality of imaging pixels 308. The imaging pixels 308 can sense atouch of a finger or the like on the display portion 301. Thus, a touchsensor can be formed using the imaging pixels 308.

Each of the pixels 302 includes a plurality of sub-pixels (e.g., asub-pixel 302R). In addition, in the sub-pixels, light-emitting elementsand pixel circuits that can supply electric power for driving thelight-emitting elements are provided.

The pixel circuits are electrically connected to wirings through whichselection signals are supplied and wirings through which image signalsare supplied.

Furthermore, the input/output device 300 is provided with a scan linedriver circuit 303 g(1) that can supply selection signals to the pixels302 and an image signal line driver circuit 303 s(1) that can supplyimage signals to the pixels 302. Note that when the image signal linedriver circuit 303 s(1) is placed in a portion other than a bendableportion, malfunction can be inhibited.

The imaging pixels 308 include photoelectric conversion elements andimaging pixel circuits that drive the photoelectric conversion elements.

The imaging pixel circuits are electrically connected to wirings throughwhich control signals are supplied and wirings through which powersupply potentials are supplied.

Examples of the control signals include a signal for selecting animaging pixel circuit from which a recorded imaging signal is read, asignal for initializing an imaging pixel circuit, and a signal fordetermining the time it takes for an imaging pixel circuit to detectlight.

The input/output device 300 is provided with an imaging pixel drivercircuit 303 g(2) that can supply control signals to the imaging pixels308 and an imaging signal line driver circuit 303 s(2) that reads outimaging signals. Note that when the imaging signal line driver circuit303 s(2) is placed in a portion other than a bendable portion,malfunction can be inhibited.

<Cross-Sectional View>

The input/output device 300 includes a substrate 310 and a countersubstrate 370 that faces the substrate 310 (see FIG. 11B).

The substrate 310 is a stacked body in which a substrate 310 b havingflexibility, a barrier film 310 a that prevents diffusion ofunintentional impurities to the light-emitting elements, and an adhesivelayer 310 c that attaches the barrier film 310 a to the substrate 310 bare stacked.

The counter substrate 370 is a stacked body including a substrate 370 bhaving flexibility, a barrier film 370 a that prevents diffusion ofunintentional impurities to the light-emitting elements, and an adhesivelayer 370 c that attaches the barrier film 370 a to the substrate 370 b(see FIG. 11B).

A sealant 360 attaches the counter substrate 370 to the substrate 310.The sealant 360, also serving as an optical adhesive layer, has arefractive index higher than that of air. The pixel circuits and thelight-emitting elements (e.g., a first light-emitting element 350R) andthe imaging pixel circuits and photoelectric conversion elements (e.g.,a photoelectric conversion element 308 p) are provided between thesubstrate 310 and the counter substrate 370.

<<Structure of Pixel>>

Each of the pixels 302 includes the sub-pixel 302R, a sub-pixel 302G,and a sub-pixel 302B (see FIG. 11C). The sub-pixel 302R includes alight-emitting module 380R, the sub-pixel 302G includes a light-emittingmodule 380G, and the sub-pixel 302B includes a light-emitting module380B.

For example, the sub-pixel 302R includes the first light-emittingelement 350R and the pixel circuit that can supply electric power to thefirst light-emitting element 350R and includes a transistor 302 t (seeFIG. 11B). Furthermore, the light-emitting module 380R includes thefirst light-emitting element 350R and an optical element (e.g., a firstcoloring layer 367R).

The first light-emitting element 350R includes a first lower electrode351R, an upper electrode 352, and a layer 353 containing alight-emitting organic compound between the first lower electrode 3518and the upper electrode 352 (see FIG. 11C).

The layer 353 containing a light-emitting organic compound includes alight-emitting unit 353 a, a light-emitting unit 353 b, and anintermediate layer 354 between the light-emitting units 353 a and 353 b.

The light-emitting module 380R includes the first coloring layer 367R onthe counter substrate 370. The coloring layer transmits light of aparticular wavelength and is, for example, a layer that selectivelytransmits light of red, green, or blue color. A region that transmitslight emitted from the light-emitting element as it is may be providedas well.

The light-emitting module 380R, for example, includes the sealant 360that is in contact with the first light-emitting element 350R and thefirst coloring layer 367R.

The first coloring layer 367R is positioned in a region overlapping withthe first light-emitting element 350R. Accordingly, part of lightemitted from the first light-emitting element 350R passes through thesealant 360 that also serves as an optical adhesive layer and throughthe first coloring layer 367R and is emitted to the outside of thelight-emitting module 380R as indicated by arrows in FIGS. 11B and 11C.

<<Structure of Input/Output Device>>

The input/output device 300 includes a light-blocking layer 367BM on thecounter substrate 370. The light-blocking layer 367BM is provided so asto surround the coloring layer (e.g., the first coloring layer 367R).

The input/output device 300 includes an anti-reflective layer 367 ppositioned in a region overlapping with the display portion 301. As theanti-reflective layer 367 p, a circular polarizing plate can be used,for example.

The input/output device 300 includes an insulating film 321. Theinsulating film 321 covers the transistor 302 t. Note that theinsulating film 321 can be used as a layer for planarizing unevennesscaused by the pixel circuits. An insulating film on which a layer thatcan prevent diffusion of impurities to the transistor 302 t and the likeis stacked can be used as the insulating film 321.

The input/output device 300 includes the light emitting elements (e.g.,the first light-emitting element 350R) over the insulating film 321.

The input/output device 300 includes, over the insulating film 321, apartition wall 328 that overlaps with an end portion of the first lowerelectrode 351R (see FIG. 11C). In addition, a spacer 329 that controlsthe distance between the substrate 310 and the counter substrate 370 isprovided on the partition wall 328. <<Structure of Image Signal LineDriver Circuit>>

The image signal line driver circuit 303 s(1) includes a transistor 303t and a capacitor 303 c. Note that the image signal line driver circuit303 s(1) can be formed in the same process and over the same substrateas those of the pixel circuits.

<<Structure of Imaging Pixel>>

The imaging pixels 308 each include a photoelectric conversion element308 p and an imaging pixel circuit for sensing light received by thephotoelectric conversion element 308 p. The imaging pixel circuitincludes a transistor 308 t.

For example, a PIN photodiode can be used as the photoelectricconversion element 308 p.

<<Other Structures>>

The input/output device 300 includes a wiring 311 through which a signalcan be supplied. The wiring 311 is provided with a terminal 319. Notethat an FPC 309(1) through which a signal such as an image signal or asynchronization signal can be supplied is electrically connected to theterminal 319. The FPC 309(1) is preferably placed in a portion otherthan a bendable portion of the input/output device 300. Moreover, theFPC 309(1) is preferably placed at almost the center of one side of aregion surrounding the display portion 301, especially a side which isfolded (a longer side in FIG. 11A). Accordingly, the distance between anexternal circuit for driving the input/output device 300 and theinput/output device 300 can be made short, resulting in easy connection.Furthermore, the center of gravity of the external circuit can be madealmost the same as that of the input/output device 300. As a result, aninformation processor can be treated easily and mistakes such asdropping can be prevented.

Note that a printed wiring board (PWB) may be attached to the FPC309(1).

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 7

In this embodiment, a structure of a display panel that can be used inthe display device of one embodiment of the present invention isdescribed with reference to FIGS. 12A and 12B and FIG. 13. Note that thedisplay panel described in this embodiment includes a touch sensor (acontact sensor device) that overlaps with a display portion; thus, thedisplay panel can be called a touch panel (an input/output device).

FIG. 12A is a schematic perspective view of a touch panel 500 describedas an example in this embodiment. Note that FIGS. 12A and 12B illustrateonly main components for simplicity. FIG. 12B is a developed view of theschematic perspective view of the touch panel 500.

FIG. 13 is a cross-sectional view of the touch panel 500 taken alongline X1-X2 in FIG. 12A.

The touch panel 500 includes a display portion 501 and a touch sensor595 (see FIG. 12B). Furthermore, the touch panel 500 includes asubstrate 510, a substrate 570, and a substrate 590. Note that thesubstrate 510, the substrate 570, and the substrate 590 each haveflexibility.

The display portion 501 includes the substrate 510, a plurality ofpixels over the substrate 510, and a plurality of wirings 511 throughwhich signals are supplied to the pixels. The plurality of wirings 511is led to a peripheral portion of the substrate 510, and part of theplurality of wirings 511 forms a terminal 519. The terminal 519 iselectrically connected to an FPC 509(1).

<Touch Sensor>

The substrate 590 includes the touch sensor 595 and a plurality ofwirings 598 electrically connected to the touch sensor 595. Theplurality of wirings 598 is led to a peripheral portion of the substrate590, and part of the plurality of wirings 598 forms a terminal forelectrical connection to an FPC 509(2). Note that in FIG. 12B,electrodes, wirings, and the like of the touch sensor 595 provided onthe back side of the substrate 590 (the side opposite to the viewerside) are indicated by solid lines for clarity.

As a touch sensor used as the touch sensor 595, a capacitive touchsensor is preferably used. Examples of the capacitive touch sensor are asurface capacitive touch sensor and a projected capacitive touch sensor.Examples of the projected capacitive touch sensor are a self capacitivetouch sensor and a mutual capacitive touch sensor, which differ mainlyin the driving method. The use of a mutual capacitive touch sensor ispreferable because multiple points can be sensed simultaneously.

An example of using a projected capacitive touch sensor is describedbelow with reference to FIG. 12B. Note that a variety of sensors thatcan sense the closeness or the contact of a sensing target such as afinger can be used.

The projected capacitive touch sensor 595 includes electrodes 591 andelectrodes 592. The electrodes 591 are electrically connected to any ofthe plurality of wirings 598, and the electrodes 592 are electricallyconnected to any of the other wirings 598.

The electrode 592 is in the form of a series of quadrangles arranged inone direction as illustrated in FIGS. 12A and 12B. Each of theelectrodes 591 is in the form of a quadrangle. A wiring 594 electricallyconnects two electrodes 591 arranged in a direction intersecting withthe direction in which the electrode 592 extends. The intersecting areaof the electrode 592 and the wiring 594 is preferably as small aspossible. Such a structure allows a reduction in the area of a regionwhere the electrodes are not provided, reducing unevenness intransmittance. As a result, unevenness in luminance of light from thetouch sensor 595 can be reduced.

Note that the shapes of the electrodes 591 and the electrodes 592 arenot limited to the above-mentioned shapes and can be any of a variety ofshapes. For example, the plurality of electrodes 591 may be provided sothat space between the electrodes 591 are reduced as much as possible,and a plurality of electrodes 592 may be provided with an insulatinglayer sandwiched between the electrodes 591 and the electrodes 592 andmay be spaced apart from each other to form a region not overlappingwith the electrodes 591. In that case, between two adjacent electrodes592, it is preferable to provide a dummy electrode which is electricallyinsulated from these electrodes, whereby the area of a region having adifferent transmittance can be reduced.

The structure of the touch panel 500 is described with reference to FIG.13.

The touch sensor 595 includes the substrate 590, the electrodes 591 andthe electrodes 592 provided in a staggered arrangement on the substrate590, an insulating layer 593 covering the electrodes 591 and theelectrodes 592, and the wiring 594 that electrically connects theadjacent electrodes 591 to each other.

An adhesive layer 597 attaches the substrate 590 to the substrate 570 sothat the touch sensor 595 overlaps with the display portion 501.

The electrodes 591 and the electrodes 592 are formed using alight-transmitting conductive material. As a light-transmittingconductive material, a conductive oxide such as indium oxide, indium tinoxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium isadded can be used.

The electrodes 591 and the electrodes 592 may be formed by depositing alight-transmitting conductive material on the substrate 590 by asputtering method and then removing an unnecessary portion by any ofvarious patterning techniques such as photolithography.

The insulating layer 593 covers the electrodes 591 and the electrodes592. Examples of a material for the insulating layer 593 are a resinsuch as acrylic or epoxy resin, a resin having a siloxane bond, and aninorganic insulating material such as silicon oxide, silicon oxynitride,or aluminum oxide.

Furthermore, openings reaching the electrodes 591 are formed in theinsulating layer 593, and the wiring 594 electrically connects theadjacent electrodes 591. The wiring 594 is preferably formed using alight-transmitting conductive material, in which case the aperture ratioof the touch panel can be increased. Moreover, the wiring 594 ispreferably formed using a material that has higher conductivity thanthose of the electrodes 591 and the electrodes 592.

One electrode 592 extends in one direction, and a plurality ofelectrodes 592 is provided in the form of stripes.

The wiring 594 intersects with the electrode 592.

Adjacent electrodes 591 are provided with one electrode 592 providedtherebetween and are electrically connected by the wiring 594.

Note that the plurality of electrodes 591 is not necessarily arranged inthe direction orthogonal to one electrode 592 and may be arranged tointersect with one electrode 592 at an angle of less than 90 degrees.

One wiring 598 is electrically connected to any of the electrodes 591and 592. Part of the wiring 598 serves as a terminal. For the wiring598, a metal material such as aluminum, gold, platinum, silver, nickel,titanium, tungsten, chromium, molybdenum, iron, cobalt, copper, orpalladium or an alloy material containing any of these metal materialscan be used.

Note that an insulating layer that covers the insulating layer 593 andthe wiring 594 may be provided to protect the touch sensor 595.

Furthermore, a connection layer 599 electrically connects the wiring 598to the FPC 509(2).

As the connection layer 599, any of various anisotropic conductive films(ACF), anisotropic conductive pastes (ACP), or the like can be used.

The adhesive layer 597 has a light-transmitting property. For example, athermosetting resin or an ultraviolet curable resin can be used;specifically, a resin such as an acrylic resin, an urethane resin, anepoxy resin, or a resin having a siloxane bond can be used.

<Display Portion>

The touch panel 500 includes a plurality of pixels arranged in a matrix.Each of the pixels includes a display element and a pixel circuit fordriving the display element.

In this embodiment, an example of using an organic electroluminescentelement that emits white light as a display element will be described;however, the display element is not limited to such element.

As the display element, for example, in addition to organicelectroluminescent elements, any of a variety of display elements suchas display elements (electronic ink) that perform display by anelectrophoretic method, an electronic liquid powder method, or the like;MEMS shutter display elements; and optical interference type MEMSdisplay elements can be used. Note that a structure suitable foremployed display elements can be selected from among a variety ofstructures of pixel circuits.

The substrate 510 is a stacked body in which a flexible substrate 510 b,a barrier film 510 a that prevents diffusion of unintentional impuritiesto the light-emitting elements, and an adhesive layer 510 c thatattaches the barrier film 510 a to the substrate 510 b are stacked.

The substrate 570 is a stacked body in which a flexible substrate 570 b,a barrier film 570 a that prevents diffusion of unintentional impuritiesto the light-emitting elements, and an adhesive layer 570 c thatattaches the barrier film 570 a to the substrate 570 b are stacked.

A sealant 560 attaches the substrate 570 to the substrate 510. Thesealant 560, also serving as an optical adhesive layer, has a refractiveindex higher than that of air. The pixel circuits and the light-emittingelements (e.g., a first light-emitting element 550R) are providedbetween the substrate 510 and the substrate 570.

<<Structure of Pixel>>

A pixel includes a sub-pixel 502R, and the sub-pixel 502R includes alight-emitting module 580R.

The sub-pixel 502R includes the first light-emitting element 550R andthe pixel circuit that can supply electric power to the firstlight-emitting element 550R and includes a transistor 502 t.Furthermore, the light-emitting module 580R includes the firstlight-emitting element 550R and an optical element (e.g., a firstcoloring layer 567R).

The first light-emitting element 550R includes a lower electrode, anupper electrode, and a layer containing a light-emitting organiccompound between the lower electrode and the upper electrode.

The light-emitting module 580R includes the first coloring layer 567R onthe counter substrate 570. The coloring layer transmits light of aparticular wavelength and is, for example, a layer that selectivelytransmits light of red, green, or blue color. A region that transmitslight emitted from the light-emitting element as it is may be providedas well.

The light-emitting module 580R includes the sealant 560 that is incontact with the first light-emitting element 550R and the firstcoloring layer 567R.

The first coloring layer 567R is positioned in a region overlapping withthe first light-emitting element 550R. Accordingly, part of lightemitted from the first light-emitting element 550R passes through thesealant 560 that also serves as an optical adhesive layer and throughthe first coloring layer 567R and is emitted to the outside of thelight-emitting module 580R as indicated by an arrow in FIG. 13.

<<Structure of Display Portion>>

The display portion 501 includes a light-blocking layer 567BM on thecounter substrate 570. The light-blocking layer 567BM is provided so asto surround the coloring layer (e.g., the first coloring layer 567R).

The display portion 501 includes an anti-reflective layer 567 ppositioned in a region overlapping with pixels. As the anti-reflectivelayer 567 p, a circular polarizing plate can be used, for example.

The display portion 501 includes an insulating film 521. The insulatingfilm 521 covers the transistor 502 t. Note that the insulating film 521can be used as a layer for planarizing unevenness caused by the pixelcircuits. An insulating film on which a layer that can prevent diffusionof impurities to the transistor 502 t and the like is stacked can beused as the insulating film 521.

The display portion 501 includes the light-emitting elements (e.g., thefirst light-emitting element 550R) over the insulating film 521.

The display portion 501 includes, over the insulating film 521, apartition wall 528 that overlaps with an end portion of the lowerelectrode. In addition, a spacer that controls the distance between thesubstrate 510 and the substrate 570 is provided on the partition wall528.

<<Structure of Image Signal Line Driver Circuit>>

An image signal line driver circuit 503 s(1) includes a transistor 503 tand a capacitor 503 c. Note that the image signal line driver circuit503 s(1) can be formed in the same process and over the same substrateas those of the pixel circuits.

<<Other Structures>>

The display portion 501 includes the wirings 511 through which signalscan be supplied. The wirings 511 are provided with the terminal 519.Note that the FPC 509(1) through which a signal such as an image signalor a synchronization signal can be supplied is electrically connected tothe terminal 519.

Note that a printed wiring board (PWB) may be attached to the FPC509(1).

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

EXPLANATION OF REFERENCE

13 a: connecting member, 13 b: connecting member, 15 a: support panel,15 b: support panel, 102: substrate, 104 a: gate electrode, 106:insulating film, 107: insulating film, 108: insulating film, 110: oxidesemiconductor film, 112: conductive film, 112 a: first electrode, 112 b:second electrode, 114: insulating film, 116: insulating film, 118:insulating film, 120: insulating film, 122 a: conductive film, 122 b:conductive film, 122 c: gate electrode, 142 a: opening, 142 d: opening,142 e: opening, 151: transistor, 200: display device, 200B: displaydevice, 200C: display device, 200D: display device, 210: controlportion, 210B: control portion, 212: synchronization signal supplyportion, 214: power supply portion, 220: image processing portion, 230:display portion, 230(1): first region, 230(2): second region, 230(1)S:region, 230 b(1): boundary, 230 b(2): boundary, 232: driver circuit,232G: scan line driver circuit, 232S: signal line driver circuit, 239:sign, 240: sensing portion, 300: input-output device, 301: displayportion, 302: pixel, 302B: sub-pixel, 302G: sub-pixel, 302R: sub-pixel,302 t: transistor, 303 c: capacitor, 303 g(1): scan line driver circuit,303 g(2): imaging pixel driver circuit, 303 s(1): image signal linedriver circuit, 303 s(2): imaging signal line driver circuit, 303 t:transistor, 308: imaging pixel, 308 p: photoelectric conversion element,308 t: transistor, 309: FPC, 310: substrate, 310 a: barrier film, 310 b:substrate, 310 c: adhesive layer, 311: wiring, 319: terminal, 321:insulating film, 328: partition wall, 329: spacer, 350R: light-emittingelement, 351R: lower electrode, 352: upper electrode, 353: layer, 353 a:light-emitting unit, 353 b: light-emitting unit, 354: intermediatelayer, 360: sealant, 367BM: light-blocking layer, 367 p: anti-reflectivelayer, 367R: coloring layer, 370: counter substrate, 370 a: barrierfilm, 370 b: substrate, 370 c: adhesive layer, 380B: light-emittingmodule, 380G: light-emitting module, 380R: light-emitting module, 500:touch panel, 501: display portion, 502R: sub-pixel, 502 t: transistor,503 c: capacitor, 503 s: image signal line driver circuit, 503 t:transistor, 509: FPC, 510: substrate, 510 a: barrier film, 510 b:substrate, 510 c: adhesive layer, 511: wiring, 519: terminal, 521:insulating film, 528: partition wall, 550R: light-emitting element, 560:sealant, 567BM: light-blocking layer, 567 p: anti-reflective layer,567R: coloring layer, 570: substrate, 570 a: barrier film, 570 b:substrate, 570 c: adhesive layer, 580R: light-emitting module, 590:substrate, 591: electrode, 592: electrode, 593: insulating layer, 594:wiring, 595: touch sensor, 597: adhesive layer, 598: wiring, 599:connection layer, 631 p: pixel, 634 c: capacitor, 634EL: pixel circuit,634 t: transistor, 634 t_1: transistor, 634 t_2: transistor, 635EL: ELelement, E1: high flexibility region, E2: low flexibility region.

This application is based on Japanese Patent Application serial no.2013-161577 filed with Japan Patent Office on Aug. 2, 2013, the entirecontents of which are hereby incorporated by reference.

The invention claimed is:
 1. A display device comprising: a displaypanel; a flexible printed circuit electrically connected to the displaypanel; a printed wiring board electrically connected to the flexibleprinted circuit; a housing supporting the display panel, the housingcomprising a magnet; and a first member between the housing and thedisplay panel, wherein the display panel comprises a first displayregion, a second display region, and a third display region which arenot visible in a folded state of the display device, wherein, in anunfolded state of the display device, the third display region isbetween the first display region and the second display region, whereinthe display panel is bendable in the third display region, wherein thehousing comprises a first support provided on a display side of thedisplay panel and around the first display region and a second supportprovided on the display side of the display panel and around the seconddisplay region, wherein, in the unfolded state of the display device,the third display region is between the first support and the secondsupport, wherein the first member is provided on the display side of thedisplay panel and around the first display region, the second displayregion, and the third display region, wherein, in the unfolded state ofthe display device, a portion of the first member is exposed in a regionbetween the first support and the second support, wherein the displaypanel is configured to be bent with a curvature radius of greater thanor equal to 1 mm and less than or equal to 100 mm, and wherein, in thefolded state, the folded state is maintained by magnetic force of themagnet.
 2. The display device according to claim 1, wherein the displaypanel comprises a light-emitting element, and wherein the first displayregion, the second display region, and the third display region arecontinuously connected.
 3. The display device according to claim 1,wherein the display panel comprises a transistor comprising an oxidesemiconductor layer.
 4. The display device according to claim 1,comprising a touch sensor over the display panel.
 5. The display deviceaccording to claim 1, wherein a fourth display region is visible in thefolded state of the display device, wherein, in the folded state, thefourth display region overlaps with the first display region and/or thesecond display region, and wherein, in the folded state, the fourthdisplay region is capable of displaying an image.
 6. A display devicecomprising: a display panel; a housing supporting the display panel; anda first member between the housing and the display panel, wherein thedisplay panel comprises a first display region, a second display region,and a third display region which are not visible in a folded state ofthe display device, wherein, in an unfolded state of the display device,the third display region is between the first display region and thesecond display region, wherein the display panel is bendable in thethird display region, wherein the housing comprises a first supportprovided on a display side of the display panel and around the firstdisplay region and a second support provided on the display side of thedisplay panel and around the second display region, wherein, in theunfolded state of the display device, the third display region isbetween the first support and the second support, wherein, in the foldedstate of the display device, a black image is displayed in the firstdisplay region, the second display region, and the third display region,wherein the first member is provided on the display side of the displaypanel and around the first display region, the second display region,and the third display region, and wherein, in the unfolded state of thedisplay device, a portion of the first member is exposed in a regionbetween the first support and the second support.
 7. The display deviceaccording to claim 6, wherein the display panel comprises alight-emitting element, and wherein the first display region, the seconddisplay region, and the third display region are continuously connected.8. The display device according to claim 6, wherein the display panelcomprises a transistor comprising an oxide semiconductor layer.
 9. Thedisplay device according to claim 6, comprising a touch sensor over thedisplay panel.
 10. A display device comprising: a display panel; ahousing supporting the display panel; and a first member between thehousing and the display panel, wherein the display panel comprises afirst display region, a second display region, and a third displayregion which are not visible in a folded state of the display device,wherein a fourth display region is visible in the folded state of thedisplay device, wherein, in an unfolded state of the display device, thethird display region is between the first display region and the seconddisplay region, wherein, in the folded state, the fourth display regionoverlaps with the first display region and/or the second display region,wherein, in the folded state, the fourth display region is capable ofdisplaying an image, wherein the display panel is bendable in the thirddisplay region, wherein the housing comprises a first support providedon a display side of the display panel and around the first displayregion and a second support provided on the display side of the displaypanel and around the second display region, wherein, in the unfoldedstate of the display device, the third display region is between thefirst support and the second support, wherein the first member isprovided on the display side of the display panel and around the firstdisplay region, the second display region, and the third display region,and wherein, in the unfolded state of the display device, a portion ofthe first member is exposed in a region between the first support andthe second support.
 11. The display device according to claim 10,wherein the display panel comprises a light-emitting element, andwherein the first display region, the second display region, and thethird display region are continuously connected.
 12. The display deviceaccording to claim 10, wherein the display panel comprises a transistorcomprising an oxide semiconductor layer.
 13. The display deviceaccording to claim 10, comprising a touch sensor over the display panel.14. The display device according to claim 10, wherein the housingcomprises a magnet, and wherein, in the folded state, the folded stateis maintained by magnetic force of the magnet.